diff --git a/modules/swagger-codegen/src/main/resources/php/model_generic.mustache b/modules/swagger-codegen/src/main/resources/php/model_generic.mustache
index ec90e6e3ab1..c9300084b0f 100644
--- a/modules/swagger-codegen/src/main/resources/php/model_generic.mustache
+++ b/modules/swagger-codegen/src/main/resources/php/model_generic.mustache
@@ -194,7 +194,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^pa
         {{#isEnum}}
         {{^isContainer}}
         $allowedValues = $this->{{getter}}AllowableValues();
-        if (!is_null($this->container['{{name}}']) && !in_array($this->container['{{name}}'], $allowedValues)) {
+        if (!is_null($this->container['{{name}}']) && !in_array($this->container['{{name}}'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for '{{name}}', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -274,7 +274,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^pa
         {{#isEnum}}
         {{^isContainer}}
         $allowedValues = $this->{{getter}}AllowableValues();
-        if (!is_null($this->container['{{name}}']) && !in_array($this->container['{{name}}'], $allowedValues)) {
+        if (!is_null($this->container['{{name}}']) && !in_array($this->container['{{name}}'], $allowedValues, true)) {
             return false;
         }
         {{/isContainer}}
@@ -344,7 +344,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^pa
         {{#isEnum}}
         $allowedValues = $this->{{getter}}AllowableValues();
         {{^isContainer}}
-        if ({{^required}}!is_null(${{name}}) && {{/required}}!in_array(${{{name}}}, $allowedValues)) {
+        if ({{^required}}!is_null(${{name}}) && {{/required}}!in_array(${{{name}}}, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for '{{name}}', must be one of '%s'",
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumArrays.php b/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumArrays.php
index 6720f6bb8c5..667106ab45f 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumArrays.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumArrays.php
@@ -226,7 +226,7 @@ class EnumArrays implements ModelInterface, ArrayAccess
         $invalidProperties = [];
 
         $allowedValues = $this->getJustSymbolAllowableValues();
-        if (!is_null($this->container['just_symbol']) && !in_array($this->container['just_symbol'], $allowedValues)) {
+        if (!is_null($this->container['just_symbol']) && !in_array($this->container['just_symbol'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for 'just_symbol', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -246,7 +246,7 @@ class EnumArrays implements ModelInterface, ArrayAccess
     {
 
         $allowedValues = $this->getJustSymbolAllowableValues();
-        if (!is_null($this->container['just_symbol']) && !in_array($this->container['just_symbol'], $allowedValues)) {
+        if (!is_null($this->container['just_symbol']) && !in_array($this->container['just_symbol'], $allowedValues, true)) {
             return false;
         }
         return true;
@@ -273,7 +273,7 @@ class EnumArrays implements ModelInterface, ArrayAccess
     public function setJustSymbol($just_symbol)
     {
         $allowedValues = $this->getJustSymbolAllowableValues();
-        if (!is_null($just_symbol) && !in_array($just_symbol, $allowedValues)) {
+        if (!is_null($just_symbol) && !in_array($just_symbol, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for 'just_symbol', must be one of '%s'",
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumTest.php b/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumTest.php
index 5c097931fd6..e63084d94a1 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumTest.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Model/EnumTest.php
@@ -278,7 +278,7 @@ class EnumTest implements ModelInterface, ArrayAccess
         $invalidProperties = [];
 
         $allowedValues = $this->getEnumStringAllowableValues();
-        if (!is_null($this->container['enum_string']) && !in_array($this->container['enum_string'], $allowedValues)) {
+        if (!is_null($this->container['enum_string']) && !in_array($this->container['enum_string'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for 'enum_string', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -289,7 +289,7 @@ class EnumTest implements ModelInterface, ArrayAccess
             $invalidProperties[] = "'enum_string_required' can't be null";
         }
         $allowedValues = $this->getEnumStringRequiredAllowableValues();
-        if (!is_null($this->container['enum_string_required']) && !in_array($this->container['enum_string_required'], $allowedValues)) {
+        if (!is_null($this->container['enum_string_required']) && !in_array($this->container['enum_string_required'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for 'enum_string_required', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -297,7 +297,7 @@ class EnumTest implements ModelInterface, ArrayAccess
         }
 
         $allowedValues = $this->getEnumIntegerAllowableValues();
-        if (!is_null($this->container['enum_integer']) && !in_array($this->container['enum_integer'], $allowedValues)) {
+        if (!is_null($this->container['enum_integer']) && !in_array($this->container['enum_integer'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for 'enum_integer', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -305,7 +305,7 @@ class EnumTest implements ModelInterface, ArrayAccess
         }
 
         $allowedValues = $this->getEnumNumberAllowableValues();
-        if (!is_null($this->container['enum_number']) && !in_array($this->container['enum_number'], $allowedValues)) {
+        if (!is_null($this->container['enum_number']) && !in_array($this->container['enum_number'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for 'enum_number', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -325,22 +325,22 @@ class EnumTest implements ModelInterface, ArrayAccess
     {
 
         $allowedValues = $this->getEnumStringAllowableValues();
-        if (!is_null($this->container['enum_string']) && !in_array($this->container['enum_string'], $allowedValues)) {
+        if (!is_null($this->container['enum_string']) && !in_array($this->container['enum_string'], $allowedValues, true)) {
             return false;
         }
         if ($this->container['enum_string_required'] === null) {
             return false;
         }
         $allowedValues = $this->getEnumStringRequiredAllowableValues();
-        if (!is_null($this->container['enum_string_required']) && !in_array($this->container['enum_string_required'], $allowedValues)) {
+        if (!is_null($this->container['enum_string_required']) && !in_array($this->container['enum_string_required'], $allowedValues, true)) {
             return false;
         }
         $allowedValues = $this->getEnumIntegerAllowableValues();
-        if (!is_null($this->container['enum_integer']) && !in_array($this->container['enum_integer'], $allowedValues)) {
+        if (!is_null($this->container['enum_integer']) && !in_array($this->container['enum_integer'], $allowedValues, true)) {
             return false;
         }
         $allowedValues = $this->getEnumNumberAllowableValues();
-        if (!is_null($this->container['enum_number']) && !in_array($this->container['enum_number'], $allowedValues)) {
+        if (!is_null($this->container['enum_number']) && !in_array($this->container['enum_number'], $allowedValues, true)) {
             return false;
         }
         return true;
@@ -367,7 +367,7 @@ class EnumTest implements ModelInterface, ArrayAccess
     public function setEnumString($enum_string)
     {
         $allowedValues = $this->getEnumStringAllowableValues();
-        if (!is_null($enum_string) && !in_array($enum_string, $allowedValues)) {
+        if (!is_null($enum_string) && !in_array($enum_string, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for 'enum_string', must be one of '%s'",
@@ -400,7 +400,7 @@ class EnumTest implements ModelInterface, ArrayAccess
     public function setEnumStringRequired($enum_string_required)
     {
         $allowedValues = $this->getEnumStringRequiredAllowableValues();
-        if (!in_array($enum_string_required, $allowedValues)) {
+        if (!in_array($enum_string_required, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for 'enum_string_required', must be one of '%s'",
@@ -433,7 +433,7 @@ class EnumTest implements ModelInterface, ArrayAccess
     public function setEnumInteger($enum_integer)
     {
         $allowedValues = $this->getEnumIntegerAllowableValues();
-        if (!is_null($enum_integer) && !in_array($enum_integer, $allowedValues)) {
+        if (!is_null($enum_integer) && !in_array($enum_integer, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for 'enum_integer', must be one of '%s'",
@@ -466,7 +466,7 @@ class EnumTest implements ModelInterface, ArrayAccess
     public function setEnumNumber($enum_number)
     {
         $allowedValues = $this->getEnumNumberAllowableValues();
-        if (!is_null($enum_number) && !in_array($enum_number, $allowedValues)) {
+        if (!is_null($enum_number) && !in_array($enum_number, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for 'enum_number', must be one of '%s'",
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Model/Order.php b/samples/client/petstore/php/SwaggerClient-php/lib/Model/Order.php
index 0089f45bcf7..5d6bd5f222b 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Model/Order.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Model/Order.php
@@ -237,7 +237,7 @@ class Order implements ModelInterface, ArrayAccess
         $invalidProperties = [];
 
         $allowedValues = $this->getStatusAllowableValues();
-        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues)) {
+        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for 'status', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -257,7 +257,7 @@ class Order implements ModelInterface, ArrayAccess
     {
 
         $allowedValues = $this->getStatusAllowableValues();
-        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues)) {
+        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues, true)) {
             return false;
         }
         return true;
@@ -380,7 +380,7 @@ class Order implements ModelInterface, ArrayAccess
     public function setStatus($status)
     {
         $allowedValues = $this->getStatusAllowableValues();
-        if (!is_null($status) && !in_array($status, $allowedValues)) {
+        if (!is_null($status) && !in_array($status, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for 'status', must be one of '%s'",
diff --git a/samples/client/petstore/php/SwaggerClient-php/lib/Model/Pet.php b/samples/client/petstore/php/SwaggerClient-php/lib/Model/Pet.php
index 73e73c892fc..8c78b7a553e 100644
--- a/samples/client/petstore/php/SwaggerClient-php/lib/Model/Pet.php
+++ b/samples/client/petstore/php/SwaggerClient-php/lib/Model/Pet.php
@@ -243,7 +243,7 @@ class Pet implements ModelInterface, ArrayAccess
             $invalidProperties[] = "'photo_urls' can't be null";
         }
         $allowedValues = $this->getStatusAllowableValues();
-        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues)) {
+        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues, true)) {
             $invalidProperties[] = sprintf(
                 "invalid value for 'status', must be one of '%s'",
                 implode("', '", $allowedValues)
@@ -269,7 +269,7 @@ class Pet implements ModelInterface, ArrayAccess
             return false;
         }
         $allowedValues = $this->getStatusAllowableValues();
-        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues)) {
+        if (!is_null($this->container['status']) && !in_array($this->container['status'], $allowedValues, true)) {
             return false;
         }
         return true;
@@ -416,7 +416,7 @@ class Pet implements ModelInterface, ArrayAccess
     public function setStatus($status)
     {
         $allowedValues = $this->getStatusAllowableValues();
-        if (!is_null($status) && !in_array($status, $allowedValues)) {
+        if (!is_null($status) && !in_array($status, $allowedValues, true)) {
             throw new \InvalidArgumentException(
                 sprintf(
                     "Invalid value for 'status', must be one of '%s'",
diff --git a/samples/client/petstore/php/SwaggerClient-php/phpunit.xml.dist b/samples/client/petstore/php/SwaggerClient-php/phpunit.xml.dist
index cadedbc2469..c12ee148477 100644
--- a/samples/client/petstore/php/SwaggerClient-php/phpunit.xml.dist
+++ b/samples/client/petstore/php/SwaggerClient-php/phpunit.xml.dist
@@ -14,8 +14,8 @@
 
     <filter>
         <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">./lib\Api</directory>
-            <directory suffix=".php">./lib\Model</directory>
+            <directory suffix=".php">./lib/Api</directory>
+            <directory suffix=".php">./lib/Model</directory>
         </whitelist>
     </filter>
 </phpunit>
diff --git a/samples/client/petstore/php/SwaggerClient-php/test/Model/EnumTestTest.php b/samples/client/petstore/php/SwaggerClient-php/test/Model/EnumTestTest.php
index 1a2350c6f22..a5a71a14970 100644
--- a/samples/client/petstore/php/SwaggerClient-php/test/Model/EnumTestTest.php
+++ b/samples/client/petstore/php/SwaggerClient-php/test/Model/EnumTestTest.php
@@ -83,6 +83,13 @@ class EnumTestTest extends \PHPUnit_Framework_TestCase
     {
     }
 
+    /**
+     * Test attribute "enum_string_required"
+     */
+    public function testPropertyEnumStringRequired()
+    {
+    }
+
     /**
      * Test attribute "enum_integer"
      */
diff --git a/samples/client/petstore/php/SwaggerClient-php/tests/EnumTestTest.php b/samples/client/petstore/php/SwaggerClient-php/tests/EnumTestTest.php
index 9e4ea589251..834c4703104 100644
--- a/samples/client/petstore/php/SwaggerClient-php/tests/EnumTestTest.php
+++ b/samples/client/petstore/php/SwaggerClient-php/tests/EnumTestTest.php
@@ -16,6 +16,30 @@ class EnumTestTest extends \PHPUnit_Framework_TestCase
         $this->assertSame(EnumTest::ENUM_NUMBER_MINUS_1_DOT_2, -1.2);
     }
 
+    public function testStrictValidation()
+    {
+        $enum = new EnumTest([
+            'enum_string' => 0,
+        ]);
+
+        $this->assertFalse($enum->valid());
+
+        $expected = [
+            "invalid value for 'enum_string', must be one of 'UPPER', 'lower', ''",
+            "'enum_string_required' can't be null",
+        ];
+        $this->assertSame($expected, $enum->listInvalidProperties());
+    }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     */
+    public function testThrowExceptionWhenInvalidAmbiguousValueHasPassed()
+    {
+        $enum = new EnumTest();
+        $enum->setEnumString(0);
+    }
+
     public function testNonRequiredPropertyIsOptional()
     {
         $enum = new EnumTest([