diff --git a/documentation/index.html.erb b/documentation/index.html.erb
index e41b548b..3e6cb9cb 100644
--- a/documentation/index.html.erb
+++ b/documentation/index.html.erb
@@ -842,7 +842,7 @@ Expressions
       indentation level that begins the heredoc is maintained throughout, so
       you can keep it all aligned with the body of your code.
     </p>
-    <%= code_for('heredocs') %>
+    <%= code_for('heredocs', 'html') %>
     <p>
       Double-quoted heredocs, like double-quoted strings, allow interpolation.
     </p>