diff --git a/requirements/constraints.txt b/requirements/constraints.txt
index 0d0d420..398e9d4 100644
--- a/requirements/constraints.txt
+++ b/requirements/constraints.txt
@@ -43,7 +43,7 @@ snowballstemmer==1.2.1
 solar-theme==1.3.3
 Sphinx==1.6.4
 sphinx-intl==0.9.10
-tox==2.8.2
+tox==2.9.1
 traitlets==4.3.2
 twine==1.9.1
 typed-ast==1.1.0