diff --git a/tox.ini b/tox.ini
index 5cdfe48..60b7bc7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -28,6 +28,5 @@ commands =
     pytest
     {py36,py37}: mypy axes
     {py36,py37}: prospector
-    {py36,py37}: black --check --diff axes
-setenv =
+    {py36,py37}: black -t py36 --check --diff axes
     PYTHONDONTWRITEBYTECODE=1