diff --git a/index.htm b/index.htm
index 02469a6..6f0565c 100644
--- a/index.htm
+++ b/index.htm
@@ -13,8 +13,8 @@
 <script src="polyfill/keyboard.js"></script>
 
 <!-- CodeMirror syntax highlighting - this is optional -->
-<script src="//cdnjs.cloudflare.com/ajax/libs/codemirror/4.7.0/codemirror.min.js"></script>
-<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/codemirror/4.7.0/codemirror.css">
+<script src="//cdnjs.cloudflare.com/ajax/libs/codemirror/5.3.0/codemirror.min.js"></script>
+<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/codemirror/5.3.0/codemirror.css">
 <script src="cm/basic.js"></script>
 <link rel="stylesheet" href="cm/basic.css">
 <style>