diff --git a/lib/index.js b/lib/index.js
index 275a97d..3b72e52 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -36,7 +36,7 @@
   }
 
   Storage.prototype.getItem = function (key) {
-    if (key in this) {
+    if (this.hasOwnProperty(key)) {
       return String(this[key]);
     }
     return null;