diff --git a/core/modules/views_ui/views_ui.theme.inc b/core/modules/views_ui/views_ui.theme.inc
index 1f31fee..16f6c7a 100644
--- a/core/modules/views_ui/views_ui.theme.inc
+++ b/core/modules/views_ui/views_ui.theme.inc
@@ -200,7 +200,7 @@ function theme_views_ui_build_group_filter_form($variables) {
  *   - form: A render element representing the form.
  */
 function template_preprocess_views_ui_rearrange_filter_form(&$variables) {
-  $form = $variables['form'];
+  $form = &$variables['form'];
   $rows = $ungroupable_rows = array();
   // Enable grouping only if > 1 group.
   $variables['grouping'] = count(array_keys($form['#group_options'])) > 1;