Network.player is -1 for both instances. Unique player id?

I am launching my networked game twice, once as host and once as client. Both local player objects have the ID -1, indicating they are the server's local player, although the client obviously isn't. I need a way to tell the different clients apart, but with their local player object being the same on every instance, this isn't possible the way I wanted it to happen.

You can test it like this:

 public class SomePlayerScript : NetworkBehaviour {
     void Start () {
         Debug.Log ("Local player: " + Network.player.ToString ());
     }
 }

That prints -1 on both clients.