diff --git a/infra/start.sh b/infra/start.sh
index 91593d8..0908aaa 100755
--- a/infra/start.sh
+++ b/infra/start.sh
@@ -66,7 +66,7 @@ echo "[hiy] Generated proxy/caddy.json for ${DOMAIN_SUFFIX}"
 # shells. Podman uses XDG_RUNTIME_DIR for RunRoot, events dirs, and the
 # default socket path, so we must set it to something writable before any
 # podman invocation.
-if [ -z "${XDG_RUNTIME_DIR:-}" ]; then
+if [ ! -d "${XDG_RUNTIME_DIR:-}" ] || [ ! -w "${XDG_RUNTIME_DIR:-}" ]; then
     export XDG_RUNTIME_DIR="/tmp/podman-$(id -u)"
     mkdir -p "$XDG_RUNTIME_DIR"
 fi