diff --git a/tox.ini b/tox.ini
index 73300242..c424b5f0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -23,7 +23,7 @@ setenv =
 # a broader range of Python versions than OpenStack as a whole
 deps =
   -r{toxinidir}/test-requirements.txt
-commands = stestr run --suppress-attachments {posargs}
+commands = stestr run --serial --suppress-attachments {posargs}
 
 [testenv:pep8]
 commands = pre-commit run -a