diff --git a/requirements_dev.txt b/requirements_dev.txt
index f6d4ce0..5a28a36 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -3,7 +3,7 @@ bumpversion==0.5.3
 wheel==0.34.1
 watchdog==0.10.0
 flake8==3.7.9
-tox==3.14.3
+tox==3.20.0
 coverage==5.0.3
 Sphinx==2.3.1
 cryptography==2.8