A motor vehicle has an automatic transmission with a P driving stage, a N driving stage and one or more forward and reverse driving stages. The motor vehicle also has an electrical parking brake device, and an assistance system for outputting a warning information and actuating the parking brake device during the opening of the driver's door when the P driving stage is not engaged on the gear side. According to the proposals, the warning information is output only when the parking brake device is not actuated or not actuated in an error-free manner.