diff --git a/requirements_dev.txt b/requirements_dev.txt
index c973431..26f1412 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -3,7 +3,7 @@ bump2version==0.5.10
 wheel==0.34.2
 watchdog==0.9.0
 flake8==3.7.7
-tox==3.11.1
+tox==4.21.0
 coverage==4.5.3
 twine==3.2.0
 Sphinx==3.1.2