diff -u b/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
--- b/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -303,8 +303,8 @@
 
     // Check if the specified theme is one recognized by the system.
     if (!empty($themes[$theme])) {
+      // Do not disable the default or admin theme.
       if ($theme == variable_get('theme_default', 'stark') || $theme == variable_get('admin_theme', 0)) {
-        // Don't disable the default theme.
         drupal_set_message(t('%theme is the default theme and cannot be disabled.', array('%theme' => $themes[$theme]->info['name'])), 'error');
       }
       else {