A backup washer for the cylindrical scalpel of an intraluminal surgical stapling instrument of the type used to join tubular body organs. The washer comprises an annular member of semi-rigid material having an annular groove formed therein extending from the distal surface of the washer inwardly toward the proximal surface of the washer facing the scalpel. As a result, the washer comprises two spaced annular walls joined at their proximal ends by a thin web providing a backup surface for the scalpel. When the scalpel is advanced by the surgical stapling instrument it will abut and cut through the thin web of the backup washer. When the scalpel cuts through the backup washer web the force required to further advance the scalpel abruptly and noticeably diminishes giving the surgeon clear tactile indication that the surgical staples have been implanted and clinched in the tissue of the tubular body organs being joined and that the scalpel has completely severed the excess tissue.