diff --git a/openstack/_hacking.py b/openstack/_hacking.py
index 94952630c..01b05adfc 100644
--- a/openstack/_hacking.py
+++ b/openstack/_hacking.py
@@ -14,6 +14,8 @@
 
 import re
 
+from hacking import core
+
 """
 Guidelines for writing new hacking checks
 
@@ -31,6 +33,7 @@ Guidelines for writing new hacking checks
 SETUPCLASS_RE = re.compile(r"def setUpClass\(")
 
 
+@core.flake8ext
 def assert_no_setupclass(logical_line):
     """Check for use of setUpClass
 
@@ -38,7 +41,3 @@ def assert_no_setupclass(logical_line):
     """
     if SETUPCLASS_RE.match(logical_line):
         yield (0, "O300: setUpClass not allowed")
-
-
-def factory(register):
-    register(assert_no_setupclass)
diff --git a/tox.ini b/tox.ini
index b55de9b3f..3e6f1bfd0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -45,9 +45,6 @@ commands =
     flake8
     doc8 doc/source README.rst
 
-[hacking]
-local-check-factory = openstack._hacking.factory
-
 [testenv:venv]
 deps =
     -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
@@ -119,6 +116,11 @@ ignore = H306,H4,W503
 show-source = True
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build,openstack/_services_mixin.py
 
+[flake8:local-plugins]
+extension =
+  O300 = _hacking:assert_no_setupclass
+paths = ./openstack
+
 [doc8]
 extensions = .rst, .yaml