1 files changed, 1 insertions, 0 deletions
diff --git a/tox.ini b/tox.ini
index 2112a76..6f60612 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,6 +2,7 @@
 distribute = False
 envlist = py3,pep8
 minversion = 3.18.0
+requires = tox<4
 skipsdist = True
 # this allows tox to infer the base python from the environment name
 # and override any basepython configured in this file