diff --git a/tox.ini b/tox.ini
index a4d7654cc9e..24dddc14db1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -87,7 +87,7 @@ deps = {[testenv:dsvm-fullstack]deps}
 commands =
   {toxinidir}/tools/generate_dhclient_script_for_fullstack.sh {envdir}
   {toxinidir}/tools/deploy_rootwrap.sh {toxinidir} {envdir}/etc {envdir}/bin
-  stestr run --concurrency 4 --black-regex neutron.tests.fullstack.test_securitygroup.TestSecurityGroupsSameNetwork.test_securitygroup {posargs}
+  stestr run --concurrency 3 --black-regex neutron.tests.fullstack.test_securitygroup.TestSecurityGroupsSameNetwork.test_securitygroup {posargs}
   stestr run --combine --concurrency 1 neutron.tests.fullstack.test_securitygroup.TestSecurityGroupsSameNetwork.test_securitygroup {posargs}
 
 [testenv:releasenotes]