diff --git a/requirements_dev.txt b/requirements_dev.txt
index d3d575c..4f20afc 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -9,6 +9,6 @@ coverage==4.5.1
 cryptography==2.2.2
 PyYAML==3.12
 pytest==3.6.0
-six==1.11.0
+six==1.12.0
 enum34==1.1.6
 nltk==3.3