diff --git a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
index b9704b153f4..2d5c2c91138 100644
--- a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
+++ b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
@@ -296,6 +296,9 @@ class ObjectSerializer
         if ($class === 'object') {
             settype($data, 'array');
             return $data;
+        } else if ($class === 'mixed') {
+            settype($data, gettype($data));
+            return $data;
         }
 
         if ($class === '\DateTime') {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
index 69188fda3ec..91d8beb5d51 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
@@ -305,6 +305,9 @@ class ObjectSerializer
         if ($class === 'object') {
             settype($data, 'array');
             return $data;
+        } else if ($class === 'mixed') {
+            settype($data, gettype($data));
+            return $data;
         }
 
         if ($class === '\DateTime') {