diff --git a/requirements.txt b/requirements.txt
index 857382ac..21ca2a14 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,4 +4,4 @@ pep8==1.4.5
 pyflakes>=0.7.2,<0.7.4
 flake8==2.0
 
-six
+six<1.4.0