OnTriggerEnter counts twice

I have a checkpoint system and at the end i made a empty game object with a box collider.
When the player enters it, it should show the position he finished.

The problem is when entering the collision area , it counts fast twice (you can even see the number changing from 1 to 2 , 3 to 4 etc)

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class WayPointFinishLine : MonoBehaviour {
	private int PositionNr = 0;
	public TextMesh TextM;
	void OnTriggerEnter(Collider other) { 
		PositionNr += 1;
		if (other.gameObject.tag == "Player" || other.gameObject.tag == "Player2") {
				TextM.text = "Finished '" + PositionNr + "'";



It is common problem, sometimes Triggers calling several times. I am using bool for it.