diff --git a/tox.ini b/tox.ini
index dc25be91..f2aaed24 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,7 +18,9 @@ commands = flake8 {posargs}
 [testenv]
 usedevelop = True
 install_command = pip install {opts} {packages}
-setenv = VIRTUAL_ENV={envdir}
+setenv =
+    VIRTUAL_ENV={envdir}
+    ZOOKEEPER_VERSION={env:ZOOKEEPER_VERSION:}
 deps = -r{toxinidir}/requirements.txt
     -r{toxinidir}/requirements_sphinx.txt
 commands = {toxinidir}/ensure-zookeeper-env.sh nosetests {posargs: -d -v --with-coverage kazoo.tests}