diff --git a/test-requirements.txt b/test-requirements.txt
index 702a3af..b986009 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -2,7 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-hacking<0.11,>=0.10.0
+hacking>=2.0,<2.1 # Apache-2.0
 
 coverage!=4.4,>=4.0 # Apache-2.0
 oslosphinx>=4.7.0 # Apache-2.0
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