diff --git a/requirements/constraints.txt b/requirements/constraints.txt
index 7be88d2..2e6937b 100644
--- a/requirements/constraints.txt
+++ b/requirements/constraints.txt
@@ -10,3 +10,7 @@
 
 # Common constraints for edx repos
 -c https://raw.githubusercontent.com/edx/edx-lint/master/edx_lint/files/common_constraints.txt
+
+# tox>4.0.0 isn't yet compatible with many tox plugins, causing CI failures in almost all repos.
+# Details can be found in this discussion: https://github.com/tox-dev/tox/discussions/1810
+tox<4.0.0