diff --git a/tox.ini b/tox.ini
index e8b6fba..5ae7b00 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,7 +24,8 @@
 commands = {posargs}
 
 [testenv:docs]
-commands = python setup.py build_sphinx
+commands =
+  sphinx-build -a -E -W -b html doc/source doc/build/html
 
 [testenv:releasenotes]
 commands =
@@ -32,8 +33,8 @@
 
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.
-
+# W503 line break before binary operator
 show-source = True
-ignore = E123,E125
+ignore = E123,E125,W503
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build