diff --git a/index.html b/index.html
index 3db265a..0720882 100644
--- a/index.html
+++ b/index.html
@@ -133,6 +133,7 @@
 <script src="js/util.js"></script>
 <script src="js/ext/unicode.js"></script>
 <script src="js/ext/color.js"></script>
+<script src="js/undo.js"></script>
 <script src="js/clipboard.js"></script>
 <script src="js/ext/upload.js"></script>
 <script src="js/ext/user.js"></script>