diff --git a/core/modules/system/src/Form/ThemeSettingsForm.php b/core/modules/system/src/Form/ThemeSettingsForm.php
index 7e9893c..a238f4f 100644
--- a/core/modules/system/src/Form/ThemeSettingsForm.php
+++ b/core/modules/system/src/Form/ThemeSettingsForm.php
@@ -314,9 +314,14 @@ public function buildForm(array $form, FormStateInterface $form_state, $theme =
       // Process the theme and all its base themes.
       foreach ($theme_keys as $theme) {
         // Include the theme-settings.php file.
-        $filename = DRUPAL_ROOT . '/' . $themes[$theme]->getPath() . '/theme-settings.php';
-        if (file_exists($filename)) {
-          require_once $filename;
+        $theme_settings_file = drupal_get_path('theme', $theme) . '/theme-settings.php';
+        $theme_file = drupal_get_path('theme', $theme) . '/' . $theme . '.theme';
+        $filenames = array($theme_setting_file, $theme_file);
+        foreach ($filenames as $filename) {
+          if (file_exists($filename)) {
+            require_once $filename;
+            $form_state->addBuildInfo('files', array($filename));
+          }
         }
 
         // Call theme-specific settings.