diff --git a/core/lib/Drupal/Core/Form/FormStateInterface.php b/core/lib/Drupal/Core/Form/FormStateInterface.php
index fd37fcddef0..e227ee69837 100644
--- a/core/lib/Drupal/Core/Form/FormStateInterface.php
+++ b/core/lib/Drupal/Core/Form/FormStateInterface.php
@@ -687,7 +687,7 @@ interface FormStateInterface {
    *
    * @return array
    */
-  public function getGroups();
+  public function &getGroups();
 
   /**
    * Sets that this form has a file element.