A rotating mudguard assembly having fixed and rotating parts includes a locking mechanism to limit the relative movement between the fixed and rotating parts of the assembly. The locking mechanism has a locking pin which can selectively engage with a locking plate, the pin and the plate on respective parts of the rotating mudguard assembly. The locking mechanism may be an integral part of the assembly, or the locking mechanism may be a kit of parts for installation on or retrofitting to an assembly.