diff --git a/IPython/html/static/notebook/js/main.js b/IPython/html/static/notebook/js/main.js
index 4f3b72b..ec25f23 100644
--- a/IPython/html/static/notebook/js/main.js
+++ b/IPython/html/static/notebook/js/main.js
@@ -99,6 +99,10 @@ function (marked) {
tables: true,
langPrefix: "language-",
highlight: function(code, lang) {
+ if (!lang) {
+ // no language, no highlight
+ return code;
+ }
var highlighted;
try {
highlighted = hljs.highlight(lang, code, false);