Index: includes/bootstrap.inc
===================================================================
--- includes/bootstrap.inc	(revision 856)
+++ includes/bootstrap.inc	(working copy)
@@ -975,7 +975,7 @@
   unicode_check();
   drupal_add_css(drupal_get_path('module', 'system') .'/defaults.css', 'module');
   drupal_add_css(drupal_get_path('module', 'system') .'/system.css', 'module');
-  $theme = '';
+  $theme = variable_get('custom_maintenance_theme', '');
 }
 
 /**