diff --git a/core/modules/book/lib/Drupal/book/BookBreadcrumbBuilder.php b/core/modules/book/lib/Drupal/book/BookBreadcrumbBuilder.php
index d78c054..ddb0857 100644
--- a/core/modules/book/lib/Drupal/book/BookBreadcrumbBuilder.php
+++ b/core/modules/book/lib/Drupal/book/BookBreadcrumbBuilder.php
@@ -20,12 +20,9 @@ class BookBreadcrumbBuilder implements BreadcrumbBuilderInterface {
   public function build(array $attributes) {
     // @todo This only works for legacy routes. Once node/% is converted to the
     //   new router this code will need to be updated.
-    if (isset($attributes['_drupal_menu_item'])) {
-      $node = $attributes['_drupal_menu_item']['map'][1];
-      if (isset($node->book)) {
-        // @todo Write an actual implementation.
-        return menu_get_active_breadcrumb();
-      }
+    if (isset($attributes['_drupal_menu_item']['map'][1]->book)) {
+      // @todo Write an actual implementation.
+      return menu_get_active_breadcrumb();
     }
   }