A header for a combine harvester includes a conveyor belt for conveying crop material in a conveyance direction, and an adjusting device for adjusting a tension of the conveyor belt. The adjusting device includes a cable that is movable with respect to a frame member of the header. A portion of the cable that is either directly or indirectly attached to one end of a roller for the conveyor belt extends either parallel to or substantially parallel to a tensioning direction of the conveyor belt for adjusting the tension of the conveyor belt. The conveyor belt may be an infeed conveyor belt or a lateral conveyor belt of a draper header, for example.