diff --git a/tox.ini b/tox.ini
index 8ef76a6..79c0eec 100644
--- a/tox.ini
+++ b/tox.ini
@@ -39,9 +39,10 @@
 commands = oslo_debug_helper {posargs}
 
 [flake8]
-# E123, E125 skipped as they are invalid PEP-8.
-
 show-source = True
-ignore = E123,E125,E129,H404,H405
+# W504 line break after binary operator
+# (W503 and W504 are incompatible and we need to choose one of them.
+#  Existing codes follows W503, so we disable W504.)
+ignore = W504
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build