The guide rail has a longitudinal groove arranged along its upper rail side and a cover strip which closes off the groove and bears flush against the plane of the upper rail side. The spacing between opposite groove walls of the groove is smaller than the leveled cover strip. In order to retain the cover strip, each of the groove walls are provided with an undercut and retaining strips provided at both longitudinal sides of the cover strip engage into the undercuts. The cover strip is plastically curved around an axis which is parallel to the guide rail, such that the curved cover strip is smaller than the spacing between the groove walls, and after being inserted into the longitudinal groove, the curved cover strip is leveled by means of plastic deformation, such that the retaining strips are displaced into the undercuts.