diff -u b/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php
--- b/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php
@@ -128,7 +128,8 @@
           'fragment' => $destination['fragment'],
           'absolute' => TRUE,
         ];
-        $destination = Url::fromUri($uri, $options);
+        $url = Url::fromUri($uri, $options);
+        $destination = $url->toString();
       }
     }
     return $destination;