diff --git a/modules/openapi-generator/src/main/resources/php/FormDataProcessor.mustache b/modules/openapi-generator/src/main/resources/php/FormDataProcessor.mustache
index 0ff4207c167e..2e5d5cb90b33 100644
--- a/modules/openapi-generator/src/main/resources/php/FormDataProcessor.mustache
+++ b/modules/openapi-generator/src/main/resources/php/FormDataProcessor.mustache
@@ -113,7 +113,11 @@ class FormDataProcessor
                     $currentName .= $currentSuffix;
                 }
 
-                $result[$currentName] = ObjectSerializer::toString($val);
+                if (is_resource($val)) {
+                    $result[$currentName] = $val;
+                } else {
+                    $result[$currentName] = ObjectSerializer::toString($val);
+                }
             }
 
             $currentName = $start;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/FormDataProcessor.php b/samples/client/petstore/php/OpenAPIClient-php/lib/FormDataProcessor.php
index 84e351e8351d..68b939efcd80 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/FormDataProcessor.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/FormDataProcessor.php
@@ -121,7 +121,11 @@ public static function flatten(array $source, string $start = ''): array
                     $currentName .= $currentSuffix;
                 }
 
-                $result[$currentName] = ObjectSerializer::toString($val);
+                if (is_resource($val)) {
+                    $result[$currentName] = $val;
+                } else {
+                    $result[$currentName] = ObjectSerializer::toString($val);
+                }
             }
 
             $currentName = $start;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/tests/FakeHttpClient.php b/samples/client/petstore/php/OpenAPIClient-php/tests/FakeHttpClient.php
index f5e32d4c6593..d95b5881262a 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/tests/FakeHttpClient.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/tests/FakeHttpClient.php
@@ -27,7 +27,7 @@ public function getLastRequest()
     /**
      * @param null|ResponseInterface $response
      */
-    public function setResponse(ResponseInterface $response = null)
+    public function setResponse(?ResponseInterface $response = null)
     {
         $this->response = $response;
     }
diff --git a/samples/client/petstore/php/psr-18/lib/FormDataProcessor.php b/samples/client/petstore/php/psr-18/lib/FormDataProcessor.php
index 84e351e8351d..68b939efcd80 100644
--- a/samples/client/petstore/php/psr-18/lib/FormDataProcessor.php
+++ b/samples/client/petstore/php/psr-18/lib/FormDataProcessor.php
@@ -121,7 +121,11 @@ public static function flatten(array $source, string $start = ''): array
                     $currentName .= $currentSuffix;
                 }
 
-                $result[$currentName] = ObjectSerializer::toString($val);
+                if (is_resource($val)) {
+                    $result[$currentName] = $val;
+                } else {
+                    $result[$currentName] = ObjectSerializer::toString($val);
+                }
             }
 
             $currentName = $start;