diff --git a/tox.ini b/tox.ini
index 9f17a0e33..3ac09aef5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -35,6 +35,7 @@ commands =
 [testenv:functional]
 setenv =
   OS_TEST_PATH = ./novaclient/tests/functional
+commands = python setup.py testr --testr-args='--concurrency=1 {posargs}'
 
 [testenv:cover]
 commands = python setup.py testr --coverage --testr-args='{posargs}'