diff --git a/requirements_dev.txt b/requirements_dev.txt
index b6561a8..c4c9c13 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -13,6 +13,6 @@ sphinx-rtd-theme>=0.5.0
 
 # testing
 flake8>=2.6.0
-tox==3.19.0
+tox==3.20.0
 coverage>=4.3.0
 wget>=3.2