diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index 7a01ed9..eb25e48 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -1117,7 +1117,7 @@ function book_toc($bid, $depth_limit, $exclude = array()) {
 /**
  * Prepares variables for book export templates.
  *
- * Default template: book-export-html.html.twig
+ * Default template: book-export-html.html.twig.
  *
  * @param array $variables
  *   An associative array containing:
diff --git a/core/modules/book/templates/book-export-html.html.twig b/core/modules/book/templates/book-export-html.html.twig
index 23eb49f..d874faf 100644
--- a/core/modules/book/templates/book-export-html.html.twig
+++ b/core/modules/book/templates/book-export-html.html.twig
@@ -44,7 +44,7 @@
     <div class="section-{{ i }}">
   {% endfor %}
   {{ contents }}
-  {% for i in range(1, depth-1) if depth > 1 %}
+  {% for i in 1..depth-1 if depth > 1 %}
     </div>
   {% endfor %}
   </body>