diff --git a/setup.py b/setup.py
index 3c42585..f6617c3 100644
--- a/setup.py
+++ b/setup.py
@@ -8,7 +8,8 @@
     'packages': ('skgof',),
     'install_requires': (
         'numpy>=1.10',
-        'scipy>=0.16'
+        'scipy>=0.16',
+        'six>=1.0.0'
     ),
     'tests_require': (
         'flake8-print',
diff --git a/skgof/ecdfgof.py b/skgof/ecdfgof.py
index 141743a..3ea4793 100644
--- a/skgof/ecdfgof.py
+++ b/skgof/ecdfgof.py
@@ -38,7 +38,7 @@
 from functools import partial
 
 from numpy import arange, log, sort
-from scipy._lib.six import string_types
+from six import string_types
 from scipy.stats import distributions
 
 from .addist import ad_unif