1 files changed, 3 insertions, 3 deletions
diff --git a/tox.ini b/tox.ini
index 9f1b6c296..38a521b4e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -98,10 +98,10 @@ commands =
 [flake8]
 show-source = True
 # NOTE: Default ignore list is *not* empty!
-# TODO: Enable either W503 or W504:
-# W503 line break before binary operator
 # W504 line break after binary operator
-ignore = W503,W504
+# (W503 and W504 are incompatible and we need to choose one of them.
+#  Existing codes follows W503, so we disable W504.):
+ignore = W504
 exclude=.eggs,.git,.tox,doc
 
 [testenv:lower-constraints]