Why is my OnCollisionEnter function working for enemies and not my player?

I am trying to use tags to limit the OnCollisionEnter function to only trigger when a certain type of shot collides. I have nearly identical functions on my enemies as I do on the player, yet the one on the player is not working.

On the enemy I put:

 function OnCollisionEnter(collision : Collision) {
     //Player shot hits enemy, enemy explodes, score points
     if(collision.gameObject.tag == "PlayerShot"){
         gameController.AddScore (scoreValue);
         Instantiate(explosion, transform.position, transform.rotation);
         Destroy (gameObject);
         }
     //Player collides with enemy, both die, game over
     if (collision.gameObject.tag == "Player"){
         Destroy (collision.gameObject);
         Instantiate(explosion, transform.position, transform.rotation);
         gameController.GameOver();
         Destroy (gameObject);
         }
 }

Which is working as intended. Enemies do not blow themselves up with their own shots and die when shot by the player.

On the player I have:

 function OnCollisionEnter(collision : Collision) {
     //Enemy shot hits player, player explodes, game over
     if(collision.gameObject.tag == "EnemyShot"){
         Instantiate(explosion, transform.position, transform.rotation);
         gameController.GameOver();
         Destroy (gameObject);
     }
 }

Everything is correctly tagged and I'm not getting any errors, but the enemy shots just pass right through. What am I missing?