Guide rail, in particular for a roller blind in motor vehicle

The sub-assembly consisting of a slide (12) movable in a guide rail (10) has at least one braking element (38) for the slide to engage in at least one corresponding braking slot (18) in the guide rail for locking purposes. The slide has a pivot point (30) and a support element (40) at a distance from the pivot point and which is supported under spring action on the guide rail so that the braking element is pushed into the braking slot. The support element is connected to the guide by a leaf spring, or the support element is formed in one piece with the slide by means of an elastically sprung arm (36).