diff --git a/tox.ini b/tox.ini
index e8e30d75..478b165d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -25,7 +25,7 @@ setenv = OS_TEST_PATH=./karbor/tests/fullstack
          OS_TEST_TIMEOUT=3600
 commands =
   oslo-config-generator --config-file etc/oslo-config-generator/karbor.conf --output-file etc/karbor.conf
-  stestr --test-path=./karbor/tests/fullstack run '--concurrency=4 {posargs}'
+  stestr --test-path=./karbor/tests/fullstack run '{posargs}'
   stestr slowest
 
 [testenv:pep8]