diff --git a/tox.ini b/tox.ini
index c4872dc..94c2262 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,6 +2,7 @@
 envlist = py
 
 [testenv]
+allowlist_externals = /bin/sh
 commands =
     /bin/sh t/test-unconflicted
     /bin/sh t/test-conflicted