1 files changed, 1 insertions, 0 deletions

diff --git a/tox.ini b/tox.ini
index 30cde5d4..ff3d8a9b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,7 @@
 [tox]
 envlist = py3,pep8,docs
 minversion = 3.18.0
+requires = tox<4
 skipsdist = true
 ignore_basepython_conflict = true