diff --git a/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php b/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
index 521847cfe4..55161190b8 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
@@ -532,15 +532,16 @@ public function testFormCacheDeletionUncached() {
    */
   public function testExceededFileSize() {
     $request = new Request([FormBuilderInterface::AJAX_FORM_REQUEST => TRUE]);
-    $request_stack = new RequestStack();
-    $request_stack->push($request);
+    $this->requestStack = new RequestStack();
+    $this->requestStack->push($request);
     $this->fileUpload->expects($this->once())
       ->method('getUploadMaxSize')
       ->willReturn(33554432);
-
     $form_arg = $this->getMockForm('test_form_id');
     $form_state = new FormState();
 
+    $this->formBuilder = new FormBuilder($this->formValidator, $this->formSubmitter, $this->formCache, $this->moduleHandler, $this->eventDispatcher, $this->requestStack, $this->classResolver, $this->elementInfo, $this->themeManager, $this->fileUpload, $this->csrfToken);
+
     $this->setExpectedException(BrokenPostRequestException::class);
     $this->formBuilder->buildForm($form_arg, $form_state);
   }