A device for preventing excess speed, which is caused by an energy store, of a door leaf, includes a door leaf displaceable between an open position and a closed position, an energy store coupled with the door leaf, which energy store provides energy for the closing movement of the door leaf in the event of failure of the electrical energy supply, a door drive coupled with the door leaf, wherein electrical energy can be induced in the door drive when closing movement of the door leaf takes place, and a door control, which activates the door drive and which is suitable for regulation of the speed of movement of the door leaf, wherein the door control is operable by the induced electrical energy when the electrical energy supply fails, and a method of operating an elevator door.