diff --git a/addons/mail/static/src/js/mail.js b/addons/mail/static/src/js/mail.js
index 2f6cfbdd708..ff85ce8e510 100644
--- a/addons/mail/static/src/js/mail.js
+++ b/addons/mail/static/src/js/mail.js
@@ -1196,7 +1196,7 @@ openerp.mail = function (session) {
         init: function (parent, datasets, options) {
             var self = this;
             this._super(parent, options);
-            this.MailWidget = parent.__proto__ == mail.Widget.prototype ? parent : false;
+            this.MailWidget = parent instanceof mail.Widget ? parent : false;
             this.domain = options.domain || [];
             this.context = _.extend(options.context || {});