diff --git a/requirements_dev.txt b/requirements_dev.txt
index 2433d0b..f05b1a1 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -4,7 +4,7 @@ wheel==0.32.2
 watchdog==0.9.0
 flake8==3.6.0
 coverage==4.5.3
-tox==3.8.6
+tox==3.9.0
 coverage==4.5.1
 Sphinx==2.0.1
 twine==1.12.1