diff -u b/core/includes/theme.inc b/core/includes/theme.inc
--- b/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -257,7 +257,7 @@
   if (!isset($drupal_static_fast)) {
     $drupal_static_fast['registry'] = &drupal_static('theme_get_registry');
   }
-  $theme_registry = $drupal_static_fast['registry'];
+  $theme_registry = &$drupal_static_fast['registry'];
 
   // Initialize the theme, if this is called early in the bootstrap, or after
   // static variables have been reset.