diff --git a/express/cli.ts b/express/cli.ts
index e161360..b9dbed4 100644
--- a/express/cli.ts
+++ b/express/cli.ts
@@ -30,7 +30,7 @@ function parseListenAddress(listen: string | undefined): {
     if (lastColon === -1) {
         // Just a port number
         const port = parseInt(listen, 10);
-        if (isNaN(port)) {
+        if (Number.isNaN(port)) {
             throw new Error(`Invalid listen address: ${listen}`);
         }
         return { host: defaultHost, port };
@@ -39,7 +39,7 @@ function parseListenAddress(listen: string | undefined): {
     const host = listen.slice(0, lastColon);
     const port = parseInt(listen.slice(lastColon + 1), 10);
 
-    if (isNaN(port)) {
+    if (Number.isNaN(port)) {
         throw new Error(`Invalid port in listen address: ${listen}`);
     }