diff --git a/tox.ini b/tox.ini
index f6b257d463a..ea76d8f396b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -80,7 +80,7 @@ deps =
 commands =
   {toxinidir}/tools/generate_dhclient_script_for_fullstack.sh {envdir}
   {toxinidir}/tools/deploy_rootwrap.sh {toxinidir} {envdir}/etc {envdir}/bin
-  stestr run --concurrency 3 {posargs}
+  stestr run --concurrency 2 {posargs}
 
 [testenv:dsvm-fullstack-gate]
 setenv = {[testenv:dsvm-fullstack]setenv}
@@ -88,7 +88,7 @@ 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 3 --black-regex neutron.tests.fullstack.test_securitygroup.TestSecurityGroupsSameNetwork.test_securitygroup {posargs}
+  stestr run --concurrency 2 --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]