diff --git a/core/modules/system/tests/modules/ajax_test/lib/Drupal/ajax_test/Form/AjaxTestDialogForm.php b/core/modules/system/tests/modules/ajax_test/lib/Drupal/ajax_test/Form/AjaxTestDialogForm.php
index 7f7d0da..b277a2d 100644
--- a/core/modules/system/tests/modules/ajax_test/lib/Drupal/ajax_test/Form/AjaxTestDialogForm.php
+++ b/core/modules/system/tests/modules/ajax_test/lib/Drupal/ajax_test/Form/AjaxTestDialogForm.php
@@ -17,7 +17,7 @@
 /**
  * Dummy form for testing DialogController with _form routes.
  */
-class AjaxTestDialogForm extends FormBase implements FormInterface {
+class AjaxTestDialogForm extends FormBase {
 
   /**
    * {@inheritdoc}