diff --git a/requirements_dev.txt b/requirements_dev.txt
index 9275de3..099b1d8 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -3,7 +3,7 @@ bumpversion==0.5.3
 wheel==0.31.1
 watchdog==0.9.0
 flake8==3.6.0
-tox==3.1.2
+tox==3.5.3
 coverage==4.5.1
 Sphinx==1.8.0
 cryptography==2.3.1