Closure lockout systems for surgical instruments

A surgical instrument is disclosed. The surgical instrument can include a first jaw, a second jaw, and a jaw closure lockout system. The first jaw can comprise a pivot pin slot and a slide pin slot. The second jaw can comprise an anvil and, in addition, a mounting portion comprising a pivot pin, which can be movably positioned in the pivot pin slot. A shiftable guide can be movably positioned in the first jaw and can comprise a body and a barrier wall. The body can comprise a slide pin movably positioned in the slide pin slot. The barrier wall can be aligned with a portion of the pivot pin slot when the slide pin is positioned within a range of positions in the slide pin slot, and the barrier wall can be offset from the pivot pin slot when the slide pin is positioned outside the range of positions.