diff --git a/buildman/qemu-coreos/start.sh b/buildman/qemu-coreos/start.sh
index d1bbb418e..f96acfa02 100644
--- a/buildman/qemu-coreos/start.sh
+++ b/buildman/qemu-coreos/start.sh
@@ -1,11 +1,14 @@
 #!/bin/bash
 
+VM_VOLUME_SIZE="${VM_VOLUME_SIZE:-32G}"
+VM_MEMORY="${VM_MEMORY:-8G}"
+
 set -e
 set -x
 set -o nounset
 
 mkdir -p /userdata/openstack/latest
-echo "$USERDATA" > /userdata/openstack/latest/user_data
+echo "${USERDATA}" > /userdata/openstack/latest/user_data
 
 time qemu-img resize ./coreos_production_qemu_image.img "${VM_VOLUME_SIZE}"