OnControllerColliderHit with CharacterController creates a stack overflow

Hello,

when two beings start to overlap, I want to simply move them away from each other a Little bit.
It seems to work but somehow this leads to a single overflow exception sometimes.

Code (CSharp):

1.     void OnControllerColliderHit(ControllerColliderHit hit)
2.     {
3.         if (Vector3.Distance(transform.position, hit.collider.gameObject.transform.position) < controller.radius * 1.6f)
4.         {
5.             if (hit.gameObject.CompareTag("Monster") || hit.gameObject.CompareTag("Animal") || hit.gameObject.CompareTag("NPC"))
6.             {
7.                 Vector3 direction = transform.position - hit.collider.gameObject.transform.position;
8.                 direction.Normalize();
9.                 controller.SimpleMove(direction);
10.             }
11.         }

How is there a better way? Controller is a CharacterController.

Thanks a lot