diff --git a/lib/start-server.js b/lib/start-server.js
index dc5491bfa1..fcc49acfc9 100755
--- a/lib/start-server.js
+++ b/lib/start-server.js
@@ -33,7 +33,7 @@ const program = require("commander");
 
 program.option("--port <number>", "Specify port number").parse(process.argv);
 
-const port = program.port || 3000;
+const port = parseInt(program.port, 10) || 3000;
 
 console.log("Checking if port " + port + " is free...");
 tcpPortUsed.check(port, "localhost")