A roof assembly for a vehicle comprises a stationary part for attaching the roof assembly to the vehicle's fixed roof. At least one closing element is movably supported by the stationary part and is capable of moving between a closed position within the roof opening and an open position in which the rear of the closing element is raised and the closing element is moved rearwardly. The closing element is provided with at least a retaining hook configured to hook behind a locking device on the stationary part in the closed position of the closing element to provide a mechanical lock for the closing element in upward direction.The locking device is movable between a locking position and an unlocking position. The closing element is configured to actuate the locking device to move from the unlocked to the locked position when the closing element is moved to the closed position.