diff --git a/apps/commandboard-web/server.js b/apps/commandboard-web/server.js
index 6a61e34..73be072 100644
--- a/apps/commandboard-web/server.js
+++ b/apps/commandboard-web/server.js
@@ -8,7 +8,7 @@ const appDirectory = fileURLToPath(new URL(".", import.meta.url));
 const distDirectory = resolve(appDirectory, "dist");
 const indexFile = join(distDirectory, "index.html");
 const apiServer = createCommandBoardServer();
-const port = Number(process.env.PORT ?? 4173);
+const port = readPort(process.env.PORT, 4173);
 
 const mimeTypes = {
   ".css": "text/css; charset=utf-8",
@@ -67,6 +67,11 @@ function resolveStaticPath(pathname) {
   return indexFile;
 }
 
+function readPort(value, fallback) {
+  const parsed = Number(value ?? fallback);
+  return Number.isInteger(parsed) && parsed > 0 && parsed <= 65535 ? parsed : fallback;
+}
+
 function sendFile(file, headOnly, response) {
   if (!existsSync(file)) {
     response.writeHead(500, { "content-type": "text/plain; charset=utf-8" });