diff --git a/devtools/proxy_worker.sh b/devtools/proxy_worker.sh
index ed6764a..d4afd97 100755
--- a/devtools/proxy_worker.sh
+++ b/devtools/proxy_worker.sh
@@ -15,4 +15,9 @@
 
 env=$1
 
+case $env in
+  dev|prod);;
+  *) die "usage: $0 (dev | prod)"
+esac
+
 cloud-run-proxy -host $(worker_url $env) -token $(impersonation_token $env)