A device for protecting an optical sensor of a driver-assistance system for a motor vehicle, a corresponding driver-assistance system and a corresponding assembling process are disclosed. The optical sensor includes an optic and two assembled separate subassemblies. A first subassembly is mounted so as to be able to rotate about an axis of rotation and includes a housing that is configured to at least partially receive the optical sensor and an optical element that is configured to be placed upstream of the optic of the optical sensor. A second subassembly includes an actuator that is configured to drive the first subassembly to rotate.