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 518c1e1..1712b75 100644
--- a/core/modules/book/templates/book-all-books-block.html.twig
+++ b/core/modules/book/templates/book-all-books-block.html.twig
@@ -18,7 +18,8 @@
  */
 #}
 {% for book_id, menu in book_menus %}
-  <nav id="book-block-menu-{{ book_id }}" class="book-block-menu">
+  {# @todo remove type casting once http://drupal.org/node/1970960 is fixed #}
+  <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 28de0de..23eb49f 100644
--- a/core/modules/book/templates/book-export-html.html.twig
+++ b/core/modules/book/templates/book-export-html.html.twig
@@ -40,11 +40,11 @@
       to be exported as printer-friendly HTML.
     #}
 
-  {% for i in range(1, depth-1) %}
+  {% for i in 1..depth-1 if depth > 1 %}
     <div class="section-{{ i }}">
   {% endfor %}
   {{ contents }}
-  {% for i in range(1, depth-1) %}
+  {% for i in range(1, depth-1) if depth > 1 %}
     </div>
   {% endfor %}
   </body>