diff --git a/tox.ini b/tox.ini
index ab6557f15e..6068d0af38 100644
--- a/tox.ini
+++ b/tox.ini
@@ -132,7 +132,7 @@ commands =
 [testenv:check_isort]
 skip_install = True
 deps = isort
-commands = /bin/sh -c "isort -c -df -sp setup.cfg -rc synapse tests scripts-dev scripts"
+commands = /bin/sh -c "isort -c --df --sp setup.cfg synapse tests scripts-dev scripts"
 
 [testenv:check-newsfragment]
 skip_install = True