diff --git a/setup.py b/setup.py
index e9b60e9b8249b0f34d08e4ea35b87cddc2435957..55faeecced7ab6718a0969afe1e8dc7f07202ed5 100644
--- a/setup.py
+++ b/setup.py
@@ -47,6 +47,7 @@ setup(name="pytools",
       install_requires=[
           "decorator>=3.2.0",
           "appdirs>=1.4.0",
+          "six",
           ],
 
       author="Andreas Kloeckner",