diff --git a/requirements.txt b/requirements.txt
index 7abedb00..1e6921be 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
 matplotlib>=1.3.1
 numpy>=1.7.2
 scipy>=0.9.0
-six>=1.4
+six>=1.7.3
 networkx>=1.8
 pillow>=2.1.0
 dask[array]>=0.5.0