A closure of a tank of a motor vehicle for closing a filler neck gas- and fluid-tight, having a closure fastened to a flap, the flap being fastened to a vehicle body of the motor vehicle such that it is movable into an open or closed position, the closure including a seal, which causes the closure to close against the filler neck. The tank closure should be easy for a user to handle and have a relatively simple design and be economical to manufacture. This is achieved in that the seal is electromechanically or pneumatically adjustable with the aid of an actuator.