diff -u b/core/includes/theme.inc b/core/includes/theme.inc
--- b/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1764,7 +1764,7 @@
 
   // drupal_is_front_page() might throw an exception.
   try {
-    $variables['is_front'] = Drupal::service('path.matcher')->isFrontPage();
+    $variables['is_front'] = \Drupal::service('path.matcher')->isFrontPage();
   }
   catch (Exception $e) {
     // If the database is not yet available, set default values for these