A fastening device for axially fastening a rotatably mounted threaded pin to a closing element, in particular a door, having a fastening element, which can be screwed onto the threaded pin, and having a backward-rotation prevention means for securing the screwed-on fastening element, wherein the backward-rotation prevention means has a sealing region for sealing the threaded pin with respect to the closing element. The disclosure also describes a closure actuator and a closing element incorporating the fastening device.