diff --git a/core/modules/book/templates/book-all-books-block.html.twig b/core/modules/book/templates/book-all-books-block.html.twig
index 1712b75..518c1e1 100644
--- a/core/modules/book/templates/book-all-books-block.html.twig
+++ b/core/modules/book/templates/book-all-books-block.html.twig
@@ -18,8 +18,7 @@
  */
 #}
 {% for book_id, menu in book_menus %}
-  {# @todo remove type casting once http://drupal.org/node/1970960 is fixed #}
-  <nav id="book-block-menu-{{ "" ~ book_id }}" class="book-block-menu">
+  <nav id="book-block-menu-{{ book_id }}" class="book-block-menu">
     {{ menu }}
   </nav>
 {% endfor %}
diff --git a/core/modules/book/templates/book-export-html.html.twig b/core/modules/book/templates/book-export-html.html.twig
index d874faf..95d5de3 100644
--- a/core/modules/book/templates/book-export-html.html.twig
+++ b/core/modules/book/templates/book-export-html.html.twig
@@ -19,7 +19,7 @@
  * @ingroup themeable
  */
 #}
-<!DOCTYPE html >
+<!DOCTYPE html>
 <html{{ html_attributes }}>
   <head>
     <title>{{ title }}></title>