A pneumatic riveter may include a jaw assembly (110) configured to extend around a portion of an object through which a fastener is to be driven, a lever (222) configured to be actuated to initiate rivet driving, a valve assembly portion (230) comprising a piston configured to enable progressive control of rivet driving responsive to actuation of the lever, and an unlocking assembly. The unlocking assembly may be configured to selectively inhibit operation of the lever responsive to positioning of a button (240) of the unlocking assembly in a locked position, and enable operation of the lever responsive to positioning of the button in an unlocked position.