diff --git a/docker/podman-docker.sh b/docker/podman-docker.sh
index cd07e361e0..2ce2f7da3b 100644
--- a/docker/podman-docker.sh
+++ b/docker/podman-docker.sh
@@ -1,10 +1,10 @@
 # DOCKER_HOST initialization
 
-if [ -z "$DOCKER_HOST" ]; then
+if [ -z "${DOCKER_HOST-}" ]; then
     if [ $(id -u) -eq 0 ]; then
 	export DOCKER_HOST=unix:///run/podman/podman.sock
     else
-	if [ -n "$XDG_RUNTIME_DIR" ]; then
+	if [ -n "${XDG_RUNTIME_DIR-}" ]; then
 	    export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/podman/podman.sock
 	fi
     fi