A cooler for cooling bulk material such as cement clinker may include a stationary aeration grate that is for receiving the bulk material is passably by a flow of cooling gas, a conveyor unit having conveyor planks that are disposed above the aeration grate and that for transporting the bulk material are movable in a reciprocating manner in a conveying direction and counter to the conveying direction, a seal assembly that prevents grate riddlings and is attached to the stationary aeration grate, and a drive element that drives the conveyor planks and extends through the stationary aeration grate. The seal assembly may lie against the drive element, and spacing between the seal assembly and the drive element may be adjustable. Further, a method for preventing grate riddlings in a cooler may involve in the event of wear decreasing the spacing between the seal assembly and the drive element.