A method for operating a braking device of a drive train of a vehicle, the drive train including an automatic gearbox of a vehicle, and the vehicle further having a gear-side parking lock, a service brake, and a parking brake that can be operated independently from the service brake. When a parking condition occurs, the parking lock may be engaged by a control device if the vehicle is protected from rolling away by a service brake that can be operated independently from the parking brake. The parking lock may then be configured to remain engaged until a driving condition occurs for the vehicle. This may optimize the parking lock operation in such a way that reliably prevents a disengagement impulse when the parking lock is disengaged, preventing the vehicle from rolling when entering or leaving a parked state.