diff --git a/tox.ini b/tox.ini
index 52b315b1..7c63f917 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,8 +4,14 @@ envlist = pep8,docs,py27,py3{4,5,6,7}
 [testenv]
 # See "testing behind a proxy"
 # @ https://review.openstack.org/#/q/I764ed51314c8e2d0572d1f0
-passenv = http_proxy https_proxy
-# passenv = http_proxy https_proxy _JAVA_OPTIONS
+passenv =
+  http_proxy
+  https_proxy
+  # avoids potential slip-over of java 1.9 which breaks Gerrit, without it
+  # Gerrit may start with incompatible java version.
+  JAVA_HOME
+  # uncomment to allow custom java options to be added
+  # _JAVA_OPTIONS
 
 commands =
   python -m git_review.tests.check_test_id_hashes discover --list