diff --git a/horizon/hacking/checks.py b/horizon/hacking/checks.py
index 4a61166f8e..60872bcbf4 100644
--- a/horizon/hacking/checks.py
+++ b/horizon/hacking/checks.py
@@ -15,6 +15,8 @@
 
 import re
 
+from hacking import core
+
 """
 Guidelines for writing new hacking checks
  - Use only for Horizon specific tests. OpenStack general tests
@@ -31,11 +33,8 @@ Guidelines for writing new hacking checks
 mutable_default_args = re.compile(r"^\s*def .+\((.+=\{\}|.+=\[\])")
 
 
+@core.flake8ext
 def no_mutable_default_args(logical_line):
     msg = "M322: Method's default argument shouldn't be mutable!"
     if mutable_default_args.match(logical_line):
         yield (0, msg)
-
-
-def factory(register):
-    register(no_mutable_default_args)
diff --git a/tox.ini b/tox.ini
index 4bf1a423c3..52a4902694 100644
--- a/tox.ini
+++ b/tox.ini
@@ -184,8 +184,9 @@ max_line_length = 80
 import-order-style = pep8
 application-import-names = horizon,openstack_dashboard
 
-[hacking]
-local-check-factory = horizon.hacking.checks.factory
+[flake8:local-plugins]
+extension =
+  M322 = horizon.hacking.checks:no_mutable_default_args
 
 [doc8]
 # File extensions to check