diff --git a/core/modules/comment/lib/Drupal/comment/CommentBreadcrumbBuilder.php b/core/modules/comment/lib/Drupal/comment/CommentBreadcrumbBuilder.php
index caf7913..3dc6a3e 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentBreadcrumbBuilder.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentBreadcrumbBuilder.php
@@ -37,7 +37,7 @@ public function __construct(TranslationManager $translation) {
    * {@inheritdoc}
    */
   public function build(array $attributes) {
-    if ($attributes[RouteObjectInterface::ROUTE_NAME] == 'comment_reply' && isset($attributes['node'])) {
+    if (isset($attributes[RouteObjectInterface::ROUTE_NAME]) && $attributes[RouteObjectInterface::ROUTE_NAME] == 'comment_reply' && isset($attributes['node'])) {
       $node = $attributes['node'];
       $uri = $node->uri();
       $breadcrumb[] = l($this->translation->translate('Home'), NULL);