diff --git a/modules/swagger-codegen/src/main/resources/php/api.mustache b/modules/swagger-codegen/src/main/resources/php/api.mustache
index 265854195041..7287dae8cfff 100644
--- a/modules/swagger-codegen/src/main/resources/php/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/php/api.mustache
@@ -222,6 +222,17 @@ use {{invokerPackage}}\ObjectSerializer;
         }
         {{/bodyParams}}
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                [{{#produces}}'{{{mediaType}}}'{{#hasMore}}, {{/hasMore}}{{/produces}}]
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                [{{#produces}}'{{{mediaType}}}'{{#hasMore}}, {{/hasMore}}{{/produces}}],
+                [{{#consumes}}'{{{mediaType}}}'{{#hasMore}}, {{/hasMore}}{{/consumes}}]
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -237,22 +248,14 @@ use {{invokerPackage}}\ObjectSerializer;
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                [{{#produces}}'{{{mediaType}}}'{{#hasMore}}, {{/hasMore}}{{/produces}}]
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                [{{#produces}}'{{{mediaType}}}'{{#hasMore}}, {{/hasMore}}{{/produces}}],
-                [{{#consumes}}'{{{mediaType}}}'{{#hasMore}}, {{/hasMore}}{{/consumes}}]
-            );
-        }
-
         {{#authMethods}}
         {{#isApiKey}}
         // this endpoint requires API key authentication
diff --git a/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml b/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
index af6a571b6278..f6998119c30c 100644
--- a/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
+++ b/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
@@ -872,6 +872,29 @@ paths:
           description: Output composite
           schema:
             $ref: '#/definitions/OuterComposite'
+  /fake/jsonFormData:
+    get:
+      tags:
+        - fake
+      summary: test json serialization of form data
+      description: ''
+      operationId: testJsonFormData
+      consumes:
+        - application/json
+      parameters:
+        - name: param
+          in: formData
+          description: field1
+          required: true
+          type: string
+        - name: param2
+          in: formData
+          description: field2
+          required: true
+          type: string
+      responses:
+        '200':
+          description: successful operation
 securityDefinitions:
   petstore_auth:
     type: oauth2
diff --git a/samples/client/petstore-security-test/php/.swagger-codegen/VERSION b/samples/client/petstore-security-test/php/.swagger-codegen/VERSION
new file mode 100644
index 000000000000..f9f7450d1359
--- /dev/null
+++ b/samples/client/petstore-security-test/php/.swagger-codegen/VERSION
@@ -0,0 +1 @@
+2.3.0-SNAPSHOT
\ No newline at end of file
diff --git a/samples/client/petstore-security-test/php/SwaggerClient-php/lib/Api/FakeApi.php b/samples/client/petstore-security-test/php/SwaggerClient-php/lib/Api/FakeApi.php
index 3ce9e2eb5b15..2c6ad2528525 100644
--- a/samples/client/petstore-security-test/php/SwaggerClient-php/lib/Api/FakeApi.php
+++ b/samples/client/petstore-security-test/php/SwaggerClient-php/lib/Api/FakeApi.php
@@ -123,7 +123,18 @@ class FakeApi
         if ($test_code_inject____end____rn_n_r !== null) {
             $formParams['test code inject */ ' " =end -- \r\n \n \r'] = ObjectSerializer::toFormValue($test_code_inject____end____rn_n_r);
         }
-        
+
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/json', '*_/  \" =end --']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/json', '*_/  \" =end --'],
+                ['application/json', '*_/  \" =end --']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -139,22 +150,14 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/json', '*_/  \" =end --']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/json', '*_/  \" =end --'],
-                ['application/json', '*_/  \" =end --']
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
diff --git a/samples/client/petstore/php/SwaggerClient-php/README.md b/samples/client/petstore/php/SwaggerClient-php/README.md
index 95b1260e5dc6..126db11d8a4c 100644
--- a/samples/client/petstore/php/SwaggerClient-php/README.md
+++ b/samples/client/petstore/php/SwaggerClient-php/README.md
@@ -82,6 +82,7 @@ Class | Method | HTTP request | Description
 *FakeApi* | [**testClientModel**](docs/Api/FakeApi.md#testclientmodel) | **PATCH** /fake | To test \"client\" model
 *FakeApi* | [**testEndpointParameters**](docs/Api/FakeApi.md#testendpointparameters) | **POST** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트
 *FakeApi* | [**testEnumParameters**](docs/Api/FakeApi.md#testenumparameters) | **GET** /fake | To test enum parameters
+*FakeApi* | [**testJsonFormData**](docs/Api/FakeApi.md#testjsonformdata) | **GET** /fake/jsonFormData | test json serialization of form data
 *Fake_classname_tags123Api* | [**testClassname**](docs/Api/Fake_classname_tags123Api.md#testclassname) | **PATCH** /fake_classname_test | To test class name in snake case
 *PetApi* | [**addPet**](docs/Api/PetApi.md#addpet) | **POST** /pet | Add a new pet to the store
 *PetApi* | [**deletePet**](docs/Api/PetApi.md#deletepet) | **DELETE** /pet/{petId} | Deletes a pet
diff --git a/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md b/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md
index 74ccd8ece5d1..1691f3d27a80 100644
--- a/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md
+++ b/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md
@@ -11,6 +11,7 @@ Method | HTTP request | Description
 [**testClientModel**](FakeApi.md#testClientModel) | **PATCH** /fake | To test \"client\" model
 [**testEndpointParameters**](FakeApi.md#testEndpointParameters) | **POST** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트
 [**testEnumParameters**](FakeApi.md#testEnumParameters) | **GET** /fake | To test enum parameters
+[**testJsonFormData**](FakeApi.md#testJsonFormData) | **GET** /fake/jsonFormData | test json serialization of form data
 
 
 # **fakeOuterBooleanSerialize**
@@ -370,3 +371,49 @@ No authorization required
 
 [[Back to top]](#) [[Back to API list]](../../README.md#documentation-for-api-endpoints) [[Back to Model list]](../../README.md#documentation-for-models) [[Back to README]](../../README.md)
 
+# **testJsonFormData**
+> testJsonFormData($param, $param2)
+
+test json serialization of form data
+
+
+
+### Example
+```php
+<?php
+require_once(__DIR__ . '/vendor/autoload.php');
+
+$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$param = "param_example"; // string | field1
+$param2 = "param2_example"; // string | field2
+
+try {
+    $api_instance->testJsonFormData($param, $param2);
+} catch (Exception $e) {
+    echo 'Exception when calling FakeApi->testJsonFormData: ', $e->getMessage(), PHP_EOL;
+}
+?>
+```
+
+### Parameters
+
+Name | Type | Description  | Notes
+------------- | ------------- | ------------- | -------------
+ **param** | **string**| field1 |
+ **param2** | **string**| field2 |
+
+### Return type
+
+void (empty response body)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: application/json
+ - **Accept**: Not defined
+
+[[Back to top]](#) [[Back to API list]](../../README.md#documentation-for-api-endpoints) [[Back to Model list]](../../README.md#documentation-for-models) [[Back to README]](../../README.md)
+
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Api/FakeApi.php b/samples/client/petstore/php/SwaggerClient-php/lib/Api/FakeApi.php
index c618684b7b8a..6e34e3eee653 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Api/FakeApi.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Api/FakeApi.php
@@ -126,6 +126,17 @@ class FakeApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                []
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                [],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -141,22 +152,14 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                []
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                [],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -273,6 +276,17 @@ class FakeApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                []
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                [],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -288,22 +302,14 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                []
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                [],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -420,6 +426,17 @@ class FakeApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                []
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                [],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -435,22 +452,14 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                []
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                [],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -567,6 +576,17 @@ class FakeApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                []
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                [],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -582,22 +602,14 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                []
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                [],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -718,6 +730,17 @@ class FakeApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/json'],
+                ['application/json']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -733,22 +756,14 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/json'],
-                ['application/json']
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -1004,6 +1019,17 @@ class FakeApi
             $formParams['callback'] = ObjectSerializer::toFormValue($callback);
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml; charset=utf-8', 'application/json; charset=utf-8']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml; charset=utf-8', 'application/json; charset=utf-8'],
+                ['application/xml; charset=utf-8', 'application/json; charset=utf-8']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -1019,22 +1045,14 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml; charset=utf-8', 'application/json; charset=utf-8']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml; charset=utf-8', 'application/json; charset=utf-8'],
-                ['application/xml; charset=utf-8', 'application/json; charset=utf-8']
-            );
-        }
-
         // this endpoint requires HTTP basic authentication
         if ($this->config->getUsername() !== null || $this->config->getPassword() !== null) {
             $headers['Authorization'] = 'Basic ' . base64_encode($this->config->getUsername() . ":" . $this->config->getPassword());
@@ -1183,6 +1201,17 @@ class FakeApi
             $formParams['enum_query_double'] = ObjectSerializer::toFormValue($enum_query_double);
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['*/*']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['*/*'],
+                ['*/*']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -1198,22 +1227,158 @@ class FakeApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
+
+        $query = \GuzzleHttp\Psr7\build_query($queryParams);
+        $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
+
+        $defaultHeaders = [];
+        if ($this->config->getUserAgent()) {
+            $defaultHeaders['User-Agent'] = $this->config->getUserAgent();
+        }
+
+        $headers = array_merge(
+            $defaultHeaders,
+            $headerParams,
+            $headers
+        );
+
+        $request = new Request(
+            'GET',
+            $url,
+            $headers,
+            $httpBody
+        );
+
+        try {
+
+            try {
+                $response = $this->client->send($request);
+            } catch (RequestException $e) {
+                throw new ApiException(
+                    "[{$e->getCode()}] {$e->getMessage()}",
+                    $e->getCode(),
+                    $e->getResponse() ? $e->getResponse()->getHeaders() : null
+                );
+            }
+
+            $statusCode = $response->getStatusCode();
+
+            if ($statusCode < 200 || $statusCode > 299) {
+                throw new ApiException(
+                    "[$statusCode] Error connecting to the API ($url)",
+                    $statusCode,
+                    $response->getHeaders(),
+                    $response->getBody()
+                );
+            }
+
+            return [null, $statusCode, $response->getHeaders()];
+
+        } catch (ApiException $e) {
+            switch ($e->getCode()) {
+            }
+            throw $e;
+        }
+    }
+    /**
+     * Operation testJsonFormData
+     *
+     * test json serialization of form data
+     *
+     * @param string $param field1 (required)
+     * @param string $param2 field2 (required)
+     * @throws \Swagger\Client\ApiException on non-2xx response
+     * @throws \InvalidArgumentException
+     * @return void
+     */
+    public function testJsonFormData($param, $param2)
+    {
+        $this->testJsonFormDataWithHttpInfo($param, $param2);
+    }
+
+    /**
+     * Operation testJsonFormDataWithHttpInfo
+     *
+     * test json serialization of form data
+     *
+     * @param string $param field1 (required)
+     * @param string $param2 field2 (required)
+     * @throws \Swagger\Client\ApiException on non-2xx response
+     * @throws \InvalidArgumentException
+     * @return array of null, HTTP status code, HTTP response headers (array of strings)
+     */
+    public function testJsonFormDataWithHttpInfo($param, $param2)
+    {
+        // verify the required parameter 'param' is set
+        if ($param === null) {
+            throw new \InvalidArgumentException('Missing the required parameter $param when calling testJsonFormData');
+        }
+        // verify the required parameter 'param2' is set
+        if ($param2 === null) {
+            throw new \InvalidArgumentException('Missing the required parameter $param2 when calling testJsonFormData');
+        }
+
+        $resourcePath = '/fake/jsonFormData';
+        $formParams = [];
+        $queryParams = [];
+        $headerParams = [];
+        $httpBody = '';
+        $multipart = false;
+        $returnType = '';
+
+
+
+        // form params
+        if ($param !== null) {
+            $formParams['param'] = ObjectSerializer::toFormValue($param);
+        }
+        // form params
+        if ($param2 !== null) {
+            $formParams['param2'] = ObjectSerializer::toFormValue($param2);
+        }
+
+        if ($multipart) {
             $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['*/*']
+                []
             );
         } else {
             $headers = $this->headerSelector->selectHeaders(
-                ['*/*'],
-                ['*/*']
+                [],
+                ['application/json']
             );
         }
 
+        // for model (json/xml)
+        if (isset($_tempBody)) {
+            $httpBody = $_tempBody; // $_tempBody is the method argument, if present
+
+        } elseif (count($formParams) > 0) {
+            if ($multipart) {
+                $multipartContents = [];
+                foreach ($formParams as $formParamName => $formParamValue) {
+                    $multipartContents[] = [
+                        'name' => $formParamName,
+                        'contents' => $formParamValue
+                    ];
+                }
+                $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
+
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
+            } else {
+                $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
+            }
+        }
+
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Api/Fake_classname_tags123Api.php b/samples/client/petstore/php/SwaggerClient-php/lib/Api/Fake_classname_tags123Api.php
index a587cbd023af..d501d730bbd0 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Api/Fake_classname_tags123Api.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Api/Fake_classname_tags123Api.php
@@ -130,6 +130,17 @@ class Fake_classname_tags123Api
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/json'],
+                ['application/json']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -145,22 +156,14 @@ class Fake_classname_tags123Api
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/json'],
-                ['application/json']
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Api/PetApi.php b/samples/client/petstore/php/SwaggerClient-php/lib/Api/PetApi.php
index df94ea0846f7..e1c7f0beeee7 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Api/PetApi.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Api/PetApi.php
@@ -129,6 +129,17 @@ class PetApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                ['application/json', 'application/xml']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -144,22 +155,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                ['application/json', 'application/xml']
-            );
-        }
-
         // this endpoint requires OAuth (access token)
         if ($this->config->getAccessToken() !== null) {
             $headers['Authorization'] = 'Bearer ' . $this->config->getAccessToken();
@@ -270,6 +273,17 @@ class PetApi
         }
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -285,22 +299,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
         // this endpoint requires OAuth (access token)
         if ($this->config->getAccessToken() !== null) {
             $headers['Authorization'] = 'Bearer ' . $this->config->getAccessToken();
@@ -409,6 +415,17 @@ class PetApi
 
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -424,22 +441,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
         // this endpoint requires OAuth (access token)
         if ($this->config->getAccessToken() !== null) {
             $headers['Authorization'] = 'Bearer ' . $this->config->getAccessToken();
@@ -566,6 +575,17 @@ class PetApi
 
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -581,22 +601,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
         // this endpoint requires OAuth (access token)
         if ($this->config->getAccessToken() !== null) {
             $headers['Authorization'] = 'Bearer ' . $this->config->getAccessToken();
@@ -720,6 +732,17 @@ class PetApi
         }
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -735,22 +758,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
         // this endpoint requires API key authentication
         $apiKey = $this->config->getApiKeyWithPrefix('api_key');
         if ($apiKey !== null) {
@@ -875,6 +890,17 @@ class PetApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                ['application/json', 'application/xml']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -890,22 +916,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                ['application/json', 'application/xml']
-            );
-        }
-
         // this endpoint requires OAuth (access token)
         if ($this->config->getAccessToken() !== null) {
             $headers['Authorization'] = 'Bearer ' . $this->config->getAccessToken();
@@ -1022,6 +1040,17 @@ class PetApi
             $formParams['status'] = ObjectSerializer::toFormValue($status);
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                ['application/x-www-form-urlencoded']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -1037,22 +1066,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                ['application/x-www-form-urlencoded']
-            );
-        }
-
         // this endpoint requires OAuth (access token)
         if ($this->config->getAccessToken() !== null) {
             $headers['Authorization'] = 'Bearer ' . $this->config->getAccessToken();
@@ -1171,6 +1192,17 @@ class PetApi
             $formParams['file'] = \GuzzleHttp\Psr7\try_fopen(ObjectSerializer::toFormValue($file), 'rb');
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/json'],
+                ['multipart/form-data']
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -1186,22 +1218,14 @@ class PetApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/json'],
-                ['multipart/form-data']
-            );
-        }
-
         // this endpoint requires OAuth (access token)
         if ($this->config->getAccessToken() !== null) {
             $headers['Authorization'] = 'Bearer ' . $this->config->getAccessToken();
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Api/StoreApi.php b/samples/client/petstore/php/SwaggerClient-php/lib/Api/StoreApi.php
index 42179d66ec91..35908a206713 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Api/StoreApi.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Api/StoreApi.php
@@ -128,6 +128,17 @@ class StoreApi
         }
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -143,22 +154,14 @@ class StoreApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -250,6 +253,17 @@ class StoreApi
 
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -265,22 +279,14 @@ class StoreApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/json'],
-                []
-            );
-        }
-
         // this endpoint requires API key authentication
         $apiKey = $this->config->getApiKeyWithPrefix('api_key');
         if ($apiKey !== null) {
@@ -412,6 +418,17 @@ class StoreApi
         }
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -427,22 +444,14 @@ class StoreApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -563,6 +572,17 @@ class StoreApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -578,22 +598,14 @@ class StoreApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Api/UserApi.php b/samples/client/petstore/php/SwaggerClient-php/lib/Api/UserApi.php
index 65c924fcba3e..5cd4cab7bb16 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Api/UserApi.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Api/UserApi.php
@@ -129,6 +129,17 @@ class UserApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -144,22 +155,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -261,6 +264,17 @@ class UserApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -276,22 +290,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -393,6 +399,17 @@ class UserApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -408,22 +425,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -524,6 +533,17 @@ class UserApi
         }
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -539,22 +559,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -656,6 +668,17 @@ class UserApi
         }
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -671,22 +694,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -816,6 +831,17 @@ class UserApi
 
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -831,22 +857,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -955,6 +973,17 @@ class UserApi
 
 
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -970,22 +999,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
@@ -1097,6 +1118,17 @@ class UserApi
             $_tempBody = $body;
         }
 
+        if ($multipart) {
+            $headers= $this->headerSelector->selectHeadersForMultipart(
+                ['application/xml', 'application/json']
+            );
+        } else {
+            $headers = $this->headerSelector->selectHeaders(
+                ['application/xml', 'application/json'],
+                []
+            );
+        }
+
         // for model (json/xml)
         if (isset($_tempBody)) {
             $httpBody = $_tempBody; // $_tempBody is the method argument, if present
@@ -1112,22 +1144,14 @@ class UserApi
                 }
                 $httpBody = new MultipartStream($multipartContents); // for HTTP post (form)
 
+            } elseif ($headers['Content-Type'] === 'application/json') {
+                $httpBody = \GuzzleHttp\json_encode($formParams);
+
             } else {
                 $httpBody = \GuzzleHttp\Psr7\build_query($formParams); // for HTTP post (form)
             }
         }
 
-        if ($httpBody instanceof MultipartStream) {
-            $headers= $this->headerSelector->selectHeadersForMultipart(
-                ['application/xml', 'application/json']
-            );
-        } else {
-            $headers = $this->headerSelector->selectHeaders(
-                ['application/xml', 'application/json'],
-                []
-            );
-        }
-
 
         $query = \GuzzleHttp\Psr7\build_query($queryParams);
         $url = $this->config->getHost() . $resourcePath . ($query ? '?' . $query : '');
diff --git a/samples/client/petstore/php/SwaggerClient-php/tests/ExceptionTest.php b/samples/client/petstore/php/SwaggerClient-php/tests/ExceptionTest.php
index b314b0625e1b..29a0d5d75596 100644
--- a/samples/client/petstore/php/SwaggerClient-php/tests/ExceptionTest.php
+++ b/samples/client/petstore/php/SwaggerClient-php/tests/ExceptionTest.php
@@ -6,12 +6,13 @@ use GuzzleHttp\Client;
 
 class ExceptionTest extends \PHPUnit_Framework_TestCase
 {
+    /**
+     * @expectedException \Swagger\Client\ApiException
+     * @expectedExceptionCode 404
+     * @expectedExceptionMessage http://petstore.swagger.io/INVALID_URL/store/inventory
+     */
     public function testNotFound()
     {
-        $this->expectException(ApiException::class);
-        $this->expectExceptionCode(404);
-        $this->expectExceptionMessage('http://petstore.swagger.io/INVALID_URL/store/inventory');
-
         $config = new Configuration();
         $config->setHost('http://petstore.swagger.io/INVALID_URL');
 
@@ -22,11 +23,12 @@ class ExceptionTest extends \PHPUnit_Framework_TestCase
         $api->getInventory();
     }
 
+    /**
+     * @expectedException \Swagger\Client\ApiException
+     * @expectedExceptionMessage Could not resolve host
+     */
     public function testWrongHost()
     {
-        $this->expectException(ApiException::class);
-        $this->expectExceptionMessage('Could not resolve host');
-
         $config = new Configuration();
         $config->setHost('http://wrong_host.zxc');
 
diff --git a/samples/client/petstore/php/SwaggerClient-php/tests/RequestTest.php b/samples/client/petstore/php/SwaggerClient-php/tests/RequestTest.php
new file mode 100644
index 000000000000..779ae71ab027
--- /dev/null
+++ b/samples/client/petstore/php/SwaggerClient-php/tests/RequestTest.php
@@ -0,0 +1,34 @@
+<?php
+
+namespace Swagger\Client;
+
+use Swagger\Client\Api\FakeApi;
+
+class RequestTest extends \PHPUnit_Framework_TestCase
+{
+
+    /** @var FakeApi */
+    private $api;
+    /** @var  FakeHttpClient */
+    private $fakeClient;
+
+    public function setUp()
+    {
+        $this->fakeClient = new FakeHttpClient();
+        $this->api = new Api\FakeApi($this->fakeClient);
+    }
+
+    public function testFormDataEncodingToJson()
+    {
+        $this->api->testJsonFormData('value', 'value2');
+
+        $request = $this->fakeClient->getLastRequest();
+        $contentType = $request->getHeader('Content-Type');
+        $this->assertEquals(['application/json'], $contentType);
+
+        $requestContent = $request->getBody()->getContents();
+
+        $expected = json_encode(['param' => 'value', 'param2' => 'value2']);
+        $this->assertEquals($expected, $requestContent);
+    }
+}
diff --git a/samples/client/petstore/php/SwaggerClient-php/tests/ResponseTypesTest.php b/samples/client/petstore/php/SwaggerClient-php/tests/ResponseTypesTest.php
index 7c6281aec5cb..71eda338ba90 100644
--- a/samples/client/petstore/php/SwaggerClient-php/tests/ResponseTypesTest.php
+++ b/samples/client/petstore/php/SwaggerClient-php/tests/ResponseTypesTest.php
@@ -37,13 +37,14 @@ class ResponseTypesTest extends \PHPUnit_Framework_TestCase
         $this->assertInstanceOf(Pet::class, $result);
     }
 
+    /**
+     * @expectedException \Swagger\Client\ApiException
+     * @expectedExceptionCode 400
+     */
     public function testDefinedErrorException()
     {
         $statusCode = 400;
 
-        $this->expectException(ApiException::class);
-        $this->expectExceptionCode($statusCode);
-
         $this->fakeHttpClient->setResponse(new Response($statusCode, [], '{}'));
         $this->api->getPetById(123);
     }
@@ -67,13 +68,14 @@ class ResponseTypesTest extends \PHPUnit_Framework_TestCase
 //        $this->assertInstanceOf(Error::class, $result);
 //    }
 
+    /**
+     * @expectedException \Swagger\Client\ApiException
+     * @expectedExceptionCode 404
+     */
     public function testDefaultErrorException()
     {
         $statusCode = 404;
 
-        $this->expectException(ApiException::class);
-        $this->expectExceptionCode($statusCode);
-
         $this->fakeHttpClient->setResponse(new Response($statusCode, [], '{}'));
         $this->api->getPetById(123);
     }