A backrest for a back seat of a motor vehicle is pivotable between a usage and folded position. A lateral part is arranged next to the backrest in usage position and forms a gap therebetween. A safety belt adjacent to the gap rests on a contact surface of the lateral part. A guide element is arranged in the gap and mounted in the lateral part for moving from an operative position partially projecting out of the gap and too a non-operative position completely retracted in the gap and vice versa. The guide element projects over the contact surface in the operative position. The guide element is moved from the operative position into the non-operative position against a spring force when the backrest pivots into the usage position.