A surgical stapling instrument is disclosed. The stapling instrument comprises a staple cartridge including a circular array of staple cavities defined therein and an anvil configured to deform the staples. The stapling instrument further comprises a closure drive configured to position the anvil relative to the staple cartridge and a firing drive configured to eject the staples from the staple cartridge. The closure drive includes a shaft which is extendable above the staple cartridge to permit the anvil to be attached to the shaft. In various instances, the stapling instrument is configured and arranged such that the anvil cannot be attached to the shaft unless the shaft is moved into a fully-extended position above the staple cartridge.