diff --git a/tox.ini b/tox.ini
index 7466482..e49481e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -98,7 +98,10 @@ commands =
     cp210x-program.py --version
 
 [testenv:readhex]
-passenv = CI PYTHON PYTHONIOENCODING
+passenv =
+    CI
+    PYTHON
+    PYTHONIOENCODING
 skip_install = true
 
 allowlist_externals =
@@ -115,7 +118,10 @@ commands =
     cp210x-program.py --read-cp210x -f readhex.out
 
 [testenv:read]
-passenv = CI PYTHON PYTHONIOENCODING
+passenv =
+    CI
+    PYTHON
+    PYTHONIOENCODING
 skip_install = true
 
 allowlist_externals =