diff --git a/tox.ini b/tox.ini
index acaf954..dd73570 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,6 +7,7 @@ ignore_basepython_conflict = True
 [testenv]
 basepython = python3
 usedevelop = True
+allowlist_externals = {toxinidir}/tools/tox_install.sh
 install_command = {toxinidir}/tools/tox_install.sh {env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
 deps =
   -r{toxinidir}/requirements.txt