diff --git a/tools/init-runonce b/tools/init-runonce
index c1dade5f469f283769da5c00c4f493bb8f0f4223..f55118656438e52afb295882281abbc127f0002f 100755
--- a/tools/init-runonce
+++ b/tools/init-runonce
@@ -19,7 +19,7 @@ fi
 # to be created.
 
 ARCH=$(uname -m)
-CIRROS_RELEASE=0.6.1
+CIRROS_RELEASE=${CIRROS_RELEASE:-0.6.1}
 IMAGE_PATH=/opt/cache/files/
 IMAGE_URL=https://github.com/cirros-dev/cirros/releases/download/${CIRROS_RELEASE}/
 IMAGE=cirros-${CIRROS_RELEASE}-${ARCH}-disk.img