A headbox, preferably for a paper machine, has a nozzle chamber with a slice gap, which is confined by a top and a bottom lip wall and by two side walls. The nozzle chamber is divided for the production of multi-layer fibrous stock webs into two or more machine-wide flow channels. For this purpose at least one wedge-shaped partition wall extends through the nozzle chamber from one side wall to the other, with this partition wall projecting through the slice gap in the direction of flow. Each of the two side walls is subdivided along the partition wall into two side wall sections. The partition wall is clamped between the side wall sections in the area of each side wall.