diff --git a/setup.py b/setup.py
index dd9543c..2e28605 100755
--- a/setup.py
+++ b/setup.py
@@ -96,6 +96,7 @@ setuptools.setup(
     install_requires=[
         'pycrypto >= 2.5',
         'requests',
+        'six',
     ],
     cmdclass={
         'sdist': eo_sdist,