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 1c90b8b..7f7d0da 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
@@ -8,6 +8,8 @@
 namespace Drupal\ajax_test\Form;
 
 use Drupal\Core\Form\FormInterface;
+use Drupal\Core\Form\FormBase;
+use Drupal\Component\Utility\String;
 use Drupal\Core\Ajax\AjaxResponse;
 use Drupal\Core\Ajax\OpenModalDialogCommand;
 use Drupal\Core\Ajax\OpenDialogCommand;
@@ -15,7 +17,7 @@
 /**
  * Dummy form for testing DialogController with _form routes.
  */
-class AjaxTestDialogForm implements FormInterface {
+class AjaxTestDialogForm extends FormBase implements FormInterface {
 
   /**
    * {@inheritdoc}
@@ -96,7 +98,7 @@ public function nonModal(&$form, &$form_state) {
   protected function dialog($is_modal = FALSE) {
     $content = ajax_test_dialog_contents();
     $response = new AjaxResponse();
-    $title = t('AJAX Dialog contents');
+    $title = $this->t(String::checkPlain('AJAX Dialog contents'));
     $html = drupal_render($content);
     if ($is_modal) {
       $response->addCommand(new OpenModalDialogCommand($title, $html));