node.js child fork process encoding

Sending a special characters (like ß) to forked child process in node.js does not work. It seems that child process can not read it.

I can show it on the very simple example where I am sending one character ("ß") to forked process and back.

The parrent proces

var child = fork("render.js");

child.on('message', function (m) {        
    res.send(m);
});

//this does not work, works fine with normal 's'   
child.send("ß");

setTimeout(function () {
    child.kill();
    res.send("Timeout error");
}, 5000);

And the child proces

process.on('message', function (m) {    
  process.send(m)
  process.exit();
});

For completeness, I am hosting node in IIS.