Unity jumping sound, help.

So I'm trying to make a sidescroller in Unity using 2D. I want my character to make a sound when he jumps. But if I press the jump button again in the air the sound will play but hes not jumping, I don't want this.

Here's my code...

 #pragma strict
 
 var jump : AudioClip;
 
 function Update () {
     if(Input.GetButtonDown("Jump")){
         if(!audio.isPlaying){
     
             audio.Play();
                 
         }    
     }    
 }