diff --git a/tox.ini b/tox.ini
index bf6e14a44..7bf0d34b0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -66,7 +66,9 @@ commands = {[testenv:py]commands}
 # This version should be kept in sync with the one declared in
 # tools/pinning/oldest/pyproject.toml.
 basepython = python3.10
-setenv = CERTBOT_OLDEST=1
+setenv =
+    {[testenv:py]setenv}
+    CERTBOT_OLDEST=1
 commands = {[testenv:py]commands}
 
 [testenv:cover]