The invention relates to a module for locking a motor vehicle lock. The aim of the invention is to design an easy-to-make and compact locking module for a lock. Said aim is achieved by a locking module comprising a housing, a switching nut that can be connected to a locking cylinder so as to rotate the switching nut by means of a key, and mechanism for converting a rotary movement of the switching nut into a linear movement to lock and unlock a lock. The mechanism comprises a dog which is linearly moved by a rotary movement of the switching nut. In the mounted state of the locking module, the linear movement of the dog actuates a mechanism that causes the lock to unlock or lock. In order to minimize the number of parts, the switching nut is rotatably mounted by the module housing.