A car fastening system includes a metal clip and a plastics locking body. When an insertion portion of the metal clip is completely inserted into a door module opening, at least two supporting tabs rest on an upper side of the door module and at least two first latching legs engage behind the opening. The insertion portion of the metal clip forms a receptacle for the plastics locking body. By insertion of the plastics locking body into the receptacle, at least two second latching legs are pressed elastically outwards out of an inoperative position such that the latching legs engage behind an opening in the car door. When the plastics locking body is completely inserted into the receptacle, a shifting movement of the second latching legs in order to release the engagement behind the opening in the car door is blocked by the plastics locking body.