diff --git a/requirements.txt b/requirements.txt
index 8fbb0bdf..2a2ac475 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,4 +2,4 @@
 -r requirements-qa.txt
 -r requirements-test.txt
 sphinx_rtd_theme==2.0.0
-tox==4.20.0
+tox==4.21.0