diff --git a/tools/tox_install.sh b/tools/tox_install.sh
index ad33ae5ff0..7f048e8eb3 100755
--- a/tools/tox_install.sh
+++ b/tools/tox_install.sh
@@ -24,6 +24,7 @@ cwd=$(/bin/pwd)
 > /tmp/tox_install.txt
 
 zuul_cloner () {
+    export ZUUL_BRANCH=${ZUUL_BRANCH-$BRANCH}
     echo "ZUUL CLONER" >> /tmp/tox_install.txt
     cd /tmp
     $ZUUL_CLONER --cache-dir \