diff --git a/app/assets/javascripts/initializers/initializeCommentPreview.js b/app/assets/javascripts/initializers/initializeCommentPreview.js
index 61c574136..f254a351b 100644
--- a/app/assets/javascripts/initializers/initializeCommentPreview.js
+++ b/app/assets/javascripts/initializers/initializeCommentPreview.js
@@ -1,3 +1,5 @@
+'use strict';
+
 function getAndShowPreview(markdownPreviewPane, markdownEditor) {
   function successCb(body) {
     markdownPreviewPane.classList.toggle('preview-toggle');