diff -u b/modules/system/system.admin.inc b/modules/system/system.admin.inc
--- b/modules/system/system.admin.inc
+++ b/modules/system/system.admin.inc
@@ -572,7 +572,7 @@
     // Process the theme and all its base themes.
     foreach ($theme_keys as $theme) {
       // Include the theme-settings.php file.
-      $filename = DRUPAL_ROOT . '/' . str_replace("/$theme.info", '', $themes[$theme]->filename) . '/theme-settings.php';
+      $filename = drupal_get_path('theme', $theme) . '/theme-settings.php';
       if (file_exists($filename)) {
         require_once $filename;
         $form_state['build_info']['files'][] = $filename;