diff --git a/tox.ini b/tox.ini
index 84dd978..5a06912 100644
--- a/tox.ini
+++ b/tox.ini
@@ -395,6 +395,8 @@
 
 [testenv:autopep8]
 deps = autopep8>=2.1.0
+allowlist_externals =
+    {toxinidir}/tools/format.sh
 commands =
     {toxinidir}/tools/format.sh