diff --git a/tox.ini b/tox.ini
index aa2fa79f20..2666e5b32e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -22,7 +22,7 @@ deps =
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
 commands =
-    stestr run --slowest {posargs}
+    stestr run --slowest --parallel-class {posargs}
 passenv = http_proxy
           HTTP_PROXY
           https_proxy
@@ -67,7 +67,7 @@ setenv = VIRTUAL_ENV={envdir}
          PYTHON=coverage run --source ironic --omit='*tests*' --parallel-mode
 commands =
   coverage erase
-  stestr run {posargs}
+  stestr run --parallel-class {posargs}
   coverage combine
   coverage report --omit='*tests*'
   coverage html -d ./cover --omit='*tests*'