diff --git a/lib/hexUtils.js b/lib/hexUtils.js
index <HASH>..<HASH> 100644
--- a/lib/hexUtils.js
+++ b/lib/hexUtils.js
@@ -1,3 +1,5 @@
+'use strict'
+
 const ethjsUtil = require('ethjs-util')
 
 module.exports = {
Allow let in hexUtils