diff -u b/core/lib/Drupal/Core/Render/Element/Actions.php b/core/lib/Drupal/Core/Render/Element/Actions.php
--- b/core/lib/Drupal/Core/Render/Element/Actions.php
+++ b/core/lib/Drupal/Core/Render/Element/Actions.php
@@ -33,8 +33,6 @@
     $class = get_class($this);
     return [
       '#process' => [
-        // @todo Move this to #pre_render.
-        [$class, 'preRenderActionsDropbutton'],
         [$class, 'processActions'],
         [$class, 'processContainer'],
       ],
@@ -85,7 +83,7 @@
    *   The pre-rendered #type 'actions' element, including individual buttons
    *   grouped into new #type 'dropbutton' elements.
    */
-  public static function preRenderActionsDropbutton(&$element) {
+  public static function preRenderActionsDropbutton($element) {
     $dropbuttons = [];
     foreach (Element::children($element, TRUE) as $key) {
       if (isset($element[$key]['#dropbutton'])) {