diff --git a/tox.ini b/tox.ini
index 6a9057b..2f305bc 100644
--- a/tox.ini
+++ b/tox.ini
@@ -51,6 +51,8 @@ description = Enforce quality standards under {basepython}
 skip_install = true
 deps =
     pre-commit
+set_env =
+    PIP_CONSTRAINT = /dev/null
 commands =
     pre-commit run --show-diff-on-failure --all-files