diff --git a/core/modules/book/lib/Drupal/book/Controller/BookController.php b/core/modules/book/lib/Drupal/book/Controller/BookController.php
index 9e27cd4..b7b665f 100644
--- a/core/modules/book/lib/Drupal/book/Controller/BookController.php
+++ b/core/modules/book/lib/Drupal/book/Controller/BookController.php
@@ -143,8 +143,8 @@ public function bookExport($type, NodeInterface $node) {
       throw new NotFoundHttpException();
     }
 
-    $rendered_html = drupal_render($this->bookExport->{$method}($node));
-    return new Response($rendered_html);
+    $exported_book = $this->bookExport->{$method}($node);
+    return new Response(drupal_render($exported_book));
   }
 
 }