diff --git a/tox.ini b/tox.ini
index 45eb1a06f5..9a296708bf 100644
--- a/tox.ini
+++ b/tox.ini
@@ -10,8 +10,6 @@ envlist = py35, py36, py37-npy{115,116,latest}, docs
 install_command = pip install --no-binary=numcodecs {opts} {packages}
 setenv =
     PYTHONHASHSEED = 42
-    # hooks for coverage exclusions based on Python major version
-    py35,py36,py37: PY_MAJOR_VERSION = py3
 passenv =
     ZARR_TEST_ABS
     ZARR_TEST_MONGO