diff --git a/tox.ini b/tox.ini
index b8ef4295ba5a904f7550d4b328ca806814a1f7c7..fc2e4f24b6e4e9e1cfc5957985b3df284df2c392 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,9 +1,14 @@
 [tox]
+requires =
+  tox>4
 envlist=flake8,black
 
 [testenv]
 basepython = python3
-passenv = SPHINXOPTS,SPHINXOPTCOLOR,JAVA_HOME
+passenv =
+  SPHINXOPTS
+  SPHINXOPTCOLOR
+  JAVA_HOME
 
 [testenv:sphinx]
 extras =