diff --git a/tox.ini b/tox.ini
index 1f104ed226..0bdd4c66b8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -58,7 +58,7 @@ basepython = python2.7
 commands =
      {[testenv]commands}
      coverage erase
-     python setup.py testr --coverage --no-parallel
+     python setup.py testr --coverage --testr-args="--concurrency=1"
      coverage run -a run_tests.py
      coverage html
      coverage xml