diff --git a/requirements_dev.txt b/requirements_dev.txt
index 638fb1c..d4b9391 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -3,7 +3,7 @@ bumpversion==0.5.3
 wheel==0.29.0
 watchdog==0.8.3
 flake8==3.4.1
-tox==2.7.0
+tox==3.9.0
 coverage==4.4.1
 Sphinx==1.6.3
 cryptography==2.0.3