diff --git a/platform/firefox/vapi-background.js b/platform/firefox/vapi-background.js
index e8a8d28b2..d257f26dc 100644
--- a/platform/firefox/vapi-background.js
+++ b/platform/firefox/vapi-background.js
@@ -195,6 +195,9 @@ vAPI.storage = {
         var key, values = [], placeholders = [];
 
         for ( key in details ) {
+            if ( !details.hasOwnProperty(key) ) {
+                continue;
+            }
             values.push(key);
             values.push(JSON.stringify(details[key]));
             placeholders.push('?, ?');
diff --git a/platform/safari/vapi-background.js b/platform/safari/vapi-background.js
index 02b62f863..6769855fa 100644
--- a/platform/safari/vapi-background.js
+++ b/platform/safari/vapi-background.js
@@ -126,6 +126,9 @@ vAPI.storage = {
 
     set: function(details, callback) {
         for ( var key in details ) {
+            if ( !details.hasOwnProperty(key) ) {
+                continue;
+            }
             this._storage.setItem(key, JSON.stringify(details[key]));
         }