diff --git a/sourcing/static/js/sourcedoc.js b/sourcing/static/js/sourcedoc.js
index cf2e711..2929929 100644
--- a/sourcing/static/js/sourcedoc.js
+++ b/sourcing/static/js/sourcedoc.js
@@ -1,3 +1,5 @@
+'use strict';
+
 function add_message() {
   $("div#messages").text("whatever");
 }