diff --git a/core/includes/theme.maintenance.inc b/core/includes/theme.maintenance.inc
index e40498c..2724220 100644
--- a/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -23,6 +23,11 @@ function _drupal_maintenance_theme() {
     return;
   }
 
+  // These are usually added from system_page_build(). When the maintenance page
+  // is themed hook_page_build is not invoked so add them here.
+  $path = drupal_get_path('module', 'system');
+  _drupal_add_css($path . '/css/system.module.css');
+  _drupal_add_css($path . '/css/system.theme.css');
   require_once __DIR__ . '/path.inc';
   require_once __DIR__ . '/theme.inc';
   require_once __DIR__ . '/common.inc';