diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index fa7d138..05ddbba 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -793,7 +793,7 @@ public function doBuildForm($form_id, &$element, FormStateInterface &$form_state
       $count++;
     }
     // Add after_build attribute to each element just to check safe markup.
-    $element['#after_build'][] = array(get_class($this), 'formSafeCheck');
+    $element['#after_build'][] = array(get_class($this), 'self::formSafeCheck');
     // The #after_build flag allows any piece of a form to be altered
     // after normal input parsing has been completed.
     if (isset($element['#after_build']) && !isset($element['#after_build_done'])) {
@@ -873,7 +873,7 @@ public function doBuildForm($form_id, &$element, FormStateInterface &$form_state
    * @return array
    *   - The form element marked as safe.
    */
-  public static function formSafeCheck(array $element, FormStateInterface $form_state) {
+  protected function formSafeCheck(array $element, FormStateInterface $form_state) {
     // Filtering keys which are expected to contain HTML.
     $markup_keys = array(
       '#description',