A grate block for a combustion grate including a block body having an upper wall which forms a bearing surface and along which the combustible material is to be conveyed and a front wall which has a lower bearing edge, the bearing edge being designed to come into contact with the bearing surface of an adjacent grate block in a feed direction, wherein the upper wall has an air supply opening formed by an air supply channel. The air supply opening is at least partially surrounded by a thickened portion which protrudes from the bearing surface, forms a protective channel extending the air supply channel, and is designed to prevent liquid from flowing into the air supply opening. A molded part for fastening to an upper wall of a block body of the grate block.