diff --git a/tox.ini b/tox.ini
index 5a9a83f79..6f79c0248 100644
--- a/tox.ini
+++ b/tox.ini
@@ -16,7 +16,7 @@ deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
-commands = stestr run {posargs}
+commands = stestr run --slowest {posargs}
 passenv =
     http_proxy
     HTTP_PROXY