An apparatus (100) includes a handle assembly, an end effector (120), a firing assembly (200), and a lockout assembly. The handle assembly includes first (102) and second (104) arms and a latching lever (180). The end effector includes first (122) and second (130) jaws and a staple cartridge (150). The firing assembly (200) is configured to actuate from a pre-fired proximal position toward a distal position in order to staple and sever tissue captured between the first jaw and the second jaw. The lockout assembly is configured to prevent distal translation of the firing assembly in a locked configuration and allow distal translation of the firing assembly in an unlocked configuration. The latching lever (180) is configured to actuate the lockout assembly from the locked configuration to the unlocked configuration in response to the latching lever pivoting the second jaw from a partially closed configuration to a fully closed configuration while the firing assembly is in the pre-fired proximal position.
