A combine harvester including a grain pan arranged to catch a crop stream from threshing or separating apparatus. The grain pan is driven in an oscillating manner to convey the crop stream rearwardly to a rear edge. A cleaning unit including a fan for generating a cleaning airstream which is directed under the rear edge of the grain pan. The grain pan comprises includes a transversely corrugated surface and longitudinal gullies having a curved profile for compensating for side-hill operation.