diff --git a/requirements.txt b/requirements.txt
index d598a4e..2ec028d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,4 +3,4 @@
 # but setuptools can't cope with conflicts in setup_requires, so thats
 # unversioned.
 pbr>=0.11
-six
+six>=1.7