diff --git a/tools/jslint/check-all.js b/tools/jslint/check-all.js
index 1db3135bcb..6ce9f4828e 100644
--- a/tools/jslint/check-all.js
+++ b/tools/jslint/check-all.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Global variables, categorized by place of definition.
 var globals =
     // Third-party libraries