An auxiliary locking drive for a motor vehicle lock having its own drive housing and being located separate from the vehicle lock in the installed state. The auxiliary locking drive can be coupled to the vehicle lock by way of a transmission that transmits a linear driving motion produced by a drive motor to the vehicle lock for transferring the vehicle lock from the half-locked state into the main locked state by the driving motion. The auxiliary locking drive, for producing the linear driving motion, has a feed gear mechanism which is connected downstream of the drive motor and is made as a spindle-spindle nut gearing with a spindle and a spindle nut.