A cleaning system in a combine harvester includes a fan producing an airstream, an oscillating upper chaffer that separates grain and smaller residue from larger non-grain particles while the airstream entrains light non-grain particles and carries them out the rear of the machine. An oscillating lower sieve receives the grain and smaller residue passing through the upper chaffer and allows grain to pass through openings while residue unable to penetrate the lower sieve travels off the end of the lower sieve and the airstream entrains light non-grain particles and carries them out of the machine. An airstream diverter located between the upper chaffer and the lower sieve redirects a portion of the airstream through lower air-flow areas of the upper chaffer. The diverter is horn-shaped with a narrow leading edge and a wider trailing edge with a concave air-directing surface between the leading and trailing edges.
