A staple cartridge unit configured for use with a surgical stapler includes a cartridge housing having a deck and a plurality of openings that house staples configured to be driven distally into tissue positioned against the deck. A knife movably disposed within the cartridge housing is configured to be driven distally through the tissue. An anvil arranged distal to the cartridge housing includes an elongate slot and a plurality of staple-forming pockets. A cutting washer is fixed relative to the anvil and includes a cutting portion disposed within the elongate slot of the anvil. The knife is movable distally to cut tissue against the cutting portion. The cutting washer includes a pair of side flanges that extend transversely to the anvil and are configured to cover a gap defined between the anvil and a distal support structure of the surgical stapler in which the staple cartridge unit is received.