diff --git a/requirements_dev.txt b/requirements_dev.txt
index 58f676e..ec92108 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -3,7 +3,7 @@ bumpversion==0.5.3
 wheel==0.31.0
 watchdog==0.8.3
 flake8==3.5.0
-tox==2.3.1
+tox==3.1.3
 coverage==4.1
 Sphinx==1.7.5
 cryptography==1.7