A rotation locking device located in the area of two separate, independent shafts or shaft sections for preventing the undesired rotation of a shaft or shaft section. The rotation locking device includes a locking pin which, in its idle position (during operation of the appliance), rests on a displacement surface of a shaft or shaft section. In the event of the undesired rotation of a shaft (caused, for example, when a tool is being unscrewed from a coupling which is connected to the shafts), the shaft underneath the locking pin turns until the pin is forced out of the displacement surface, is displaced outwards radially and pressed against a component which is fixed to the body of the appliance (e.g. the bearing sleeve of the gearbox in which the rotation locking device is fitted). Any further rotation of the shafts is prevented in this manner.