diff --git a/src/group-manager.js b/src/group-manager.js
index 60925ac..1a697e4 100644
--- a/src/group-manager.js
+++ b/src/group-manager.js
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+require('es6-shim');
+
 var vanadium = require('vanadium');
 
 var defineClass = require('./util/define-class');
diff --git a/src/invitation-manager.js b/src/invitation-manager.js
index 9b0d878..e1a26a4 100644
--- a/src/invitation-manager.js
+++ b/src/invitation-manager.js
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+require('es6-shim');
+
 var $ = require('./util/jquery');
 var defineClass = require('./util/define-class');