diff --git a/core/modules/system/lib/Drupal/system/Controller/ThemeListingController.php b/core/modules/system/lib/Drupal/system/Controller/ThemeListingController.php
index 2869c40..7198ef9 100644
--- a/core/modules/system/lib/Drupal/system/Controller/ThemeListingController.php
+++ b/core/modules/system/lib/Drupal/system/Controller/ThemeListingController.php
@@ -209,6 +209,15 @@ public function listingPage() {
     $this->moduleHandler->alter('system_themes_page', $theme_groups);
 
     $admin_form = drupal_get_form('system_themes_admin_form', $admin_theme_options);
-    return theme('system_themes_page', array('theme_groups' => $theme_groups, 'theme_group_titles' => $theme_group_titles)) . drupal_render($admin_form);
+    $build = array();
+    $build[] = array(
+      '#theme' => 'system_themes_page',
+      '#theme_groups' => $theme_groups,
+      '#theme_group_titles' => $theme_group_titles,
+    );
+    $build[] = $admin_form;
+
+    return $build;
   }
+
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 59f3dfc..568b7da 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -140,7 +140,7 @@ function system_help($path, $arg) {
 function system_theme() {
   return array_merge(drupal_common_theme(), array(
     'system_themes_page' => array(
-      'variables' => array('theme_groups' => NULL),
+      'variables' => array('theme_groups' => NULL, 'theme_group_titles' => NULL),
       'file' => 'system.admin.inc',
     ),
     'system_config_form' => array(