=== modified file 'includes/theme.maintenance.inc'
--- includes/theme.maintenance.inc	2009-11-19 15:50:23 +0000
+++ includes/theme.maintenance.inc	2009-11-21 04:09:22 +0000
@@ -46,7 +46,9 @@ function _drupal_maintenance_theme() {
       drupal_load('module', 'filter');
     }
 
-    $custom_theme = variable_get('maintenance_theme', 'minnelli');
+    // We use the default theme as the maintenance theme. If a default theme
+    // isn't specified in the database or in settings.php, we use Minnelli.
+    $custom_theme = variable_get('maintenance_theme', variable_get('theme_default', 'minnelli'));
   }
 
   $themes = list_themes();