diff --git a/tox.ini b/tox.ini
index 8efa749b0..da0e4d320 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,6 +5,7 @@ skip_missing_interpreters=true
 skipsdist=true
 
 [testenv]
+allowlist_externals={toxinidir}/.tox-install.sh
 # always re-create virtual env. A special install helper is used to configure,
 # build and install packages.
 recreate=True