diff --git a/setup.py b/setup.py
index 17de25ff..0ecb9636 100644
--- a/setup.py
+++ b/setup.py
@@ -43,6 +43,7 @@
         'plone.schemaeditor',
         'plone.supermodel',
         'setuptools',
+        'six',
         'zope.browserpage',
         'zope.component',
         'zope.copy',