diff --git a/metrics.js b/metrics.js
index 9cb8eb0e6..d4d07ec0d 100644
--- a/metrics.js
+++ b/metrics.js
@@ -1,6 +1,8 @@
 /* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
 
+'use strict';
+
 var Metrics = {
   'Courier': 600,
   'Courier-Bold': 600,