diff --git a/modules/openapi-generator/src/main/resources/php/api.mustache b/modules/openapi-generator/src/main/resources/php/api.mustache
index a8da00edff9c..655ee548e5f9 100644
--- a/modules/openapi-generator/src/main/resources/php/api.mustache
+++ b/modules/openapi-generator/src/main/resources/php/api.mustache
@@ -688,6 +688,9 @@ use {{invokerPackage}}\ObjectSerializer;
         }
         {{/formParams}}
 
+        {{#isMultipart}}
+        $multipart = true;
+        {{/isMultipart}}
         $headers = $this->headerSelector->selectHeaders(
             [{{#produces}}'{{{mediaType}}}', {{/produces}}],
             $contentType,
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php
index 3167606788c9..781edf5cc79b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php
@@ -2571,6 +2571,7 @@ public function uploadFileRequest($pet_id, $additional_metadata = null, $file =
             }
         }
 
+        $multipart = true;
         $headers = $this->headerSelector->selectHeaders(
             ['application/json', ],
             $contentType,
@@ -2917,6 +2918,7 @@ public function uploadFileWithRequiredFileRequest($pet_id, $required_file, $addi
             }
         }
 
+        $multipart = true;
         $headers = $this->headerSelector->selectHeaders(
             ['application/json', ],
             $contentType,