diff --git a/requirements.txt b/requirements.txt
index 9d002744495767e1340cb68f4595ba2d0bf3bfb8..a1cc88cfe73cb6471fea8b39c4047c467d35f989 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ enum34>=1.0.4
 futures>=2.2.0
 cython>=0.23
 coverage>=4.0
+six>=1.10