diff --git a/core/themes/bartik/bartik.theme b/core/themes/bartik/bartik.theme
index 1ec5947..c1874e4 100644
--- a/core/themes/bartik/bartik.theme
+++ b/core/themes/bartik/bartik.theme
@@ -5,6 +5,8 @@
  * Functions to support theming in the Bartik theme.
  */
 
+use Drupal\Core\Template\RenderWrapper;
+
 /**
  * Implements hook_preprocess_HOOK() for html.tpl.php.
  *
@@ -84,7 +86,7 @@ function bartik_preprocess_maintenance_page(&$variables) {
   if (!$variables['db_is_active']) {
     $variables['site_name'] = '';
   }
-  $variables['styles'] = drupal_get_css();
+  $variables['styles'] = new RenderWrapper('drupal_get_css');
   // Normally we could attach libraries via hook_page_alter(), but when the
   // database is inactive it's not called so we add them here.
   $libraries = array(