diff --git a/tox.ini b/tox.ini
index 5d2b6e4..0fd470c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -28,6 +28,7 @@ allowlist_externals =
 commands =
   sphinx-autobuild \
     --open-browser \
+    --port=0 \
     --re-ignore='.*/__pycache__/.*' \
     --re-ignore='.*/.ipynb_checkpoints/.*' \
     --re-ignore='.*\.tmp' \