diff --git a/lib/util.js b/lib/util.js
index 97c5c10fd87375..b034b29b55f74a 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -159,9 +159,9 @@ function stylizeNoColor(str, styleType) {
 
 
 function arrayToHash(array) {
-  var hash = {};
+  var hash = Object.create(null);
 
-  array.forEach(function(val, idx) {
+  array.forEach(function(val) {
     hash[val] = true;
   });