diff --git a/core/modules/book/src/BookManager.php b/core/modules/book/src/BookManager.php
index d0cf791d2a..70ae7b307a 100644
--- a/core/modules/book/src/BookManager.php
+++ b/core/modules/book/src/BookManager.php
@@ -1087,6 +1087,9 @@ protected function buildBookOutlineData(array $links, array $parents = [], $dept
   protected function buildBookOutlineRecursive(&$links, $parents, $depth) {
     $tree = [];
     $node = \Drupal::routeMatch()->getParameter('node');
+    if (!($node instance of NodeInterface)) {
+      $node = $this->entityTypeManager->getStorage('node')->load($node);
+    }  
     while ($item = array_pop($links)) {
       // Check if item belongs to the current page.
       $item['is_active'] = ($node && $node->id() == $item['nid']) ? TRUE : FALSE;