diff --git a/setup.py b/setup.py
index efb0750..c9519c0 100644
--- a/setup.py
+++ b/setup.py
@@ -54,7 +54,7 @@ setup(name="wcs-olap",
       maintainer_email="bdauvergne@entrouvert.com",
       packages=find_packages(),
       include_package_data=True,
-      install_requires=['requests', 'psycopg2', 'isodate'],
+      install_requires=['requests', 'psycopg2', 'isodate', 'six'],
       entry_points={
           'console_scripts': ['wcs-olap=wcs_olap.cmd:main'],
       },
diff --git a/wcs_olap/feeder.py b/wcs_olap/feeder.py
index 9d525db..5b1c07c 100644
--- a/wcs_olap/feeder.py
+++ b/wcs_olap/feeder.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import six
 import copy
 import os
 import json
@@ -343,7 +344,7 @@ CREATE TABLE public.dates AS (SELECT
         ctx.update(self.default_ctx)
 
         def helper(o):
-            if isinstance(o, basestring):
+            if isinstance(o, six.string_types):
                 return o.format(**ctx)
             elif isinstance(o, dict):
                 return dict((k, helper(v)) for k, v in o.iteritems())