A surgical stapling apparatus (stapler) is provided. A tool assembly includes first and second jaw members. A cartridge assembly includes an actuation sled and a slide. A drive member having a working end is configured to translate through the tool assembly when the first and second jaw members are in a closed configuration. A lock assembly including a latch is movable from a locked position to an unlocked position. The latch is urged to the locked position to engage the working end to prevent distal translation of the drive member through the tool assembly. The slide is configured to move the latch from the locked position to the unlocked position upon installation of an unspent cartridge assembly onto the first jaw member. The slide is movable by the drive member upon actuation of the stapling apparatus to allow the latch to move back to the locked position.