diff --git a/requirements_dev.txt b/requirements_dev.txt
index f03b5e9..0a708b3 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -2,7 +2,7 @@ bumpversion==0.5.3
 wheel==0.31.0
 watchdog==0.8.3
 flake8==3.5.0
-tox==2.9.1
+tox==3.9.0
 coverage==4.5.1
 Sphinx==1.7.2
 PyYAML==3.12