A pneumatic riveter comprising: a jaw assembly (110, 111, 113, 115, 117) configured to extend around a portion of an object through which a fastener is to be driven; a lever (120, 220, 420, 520) configured to be actuated to initiate rivet driving, the lever (120, 220, 420, 520) comprising an operator portion (222, 422, 522), a lever arm (224, 424) and a flange (130, 226, 426, 526), the operator portion (222, 422, 522) being disposed at a front end of the lever arm (224, 424) and the flange (130, 226, 426, 526) being disposed at a rear end of the lever arm (224, 424), wherein, when the lever (120, 220, 420, 520) is actuated via the operator portion (222, 422, 522), the lever arm (224, 424) rotates to rotate the flange (130, 226, 426, 526); a valve assembly portion (230, 330, 430) comprising a piston (232, 432) configured to enable progressive control of rivet driving responsive to actuation of the lever (120, 220, 420, 520); and an unlocking assembly (240, 400, 440, 540) configured to selectively inhibit operation of the lever (120, 220, 420, 520) responsive to positioning of a button of the unlocking assembly (240, 400, 440, 540) in a locked position, and enable operation of the lever (120, 220, 420, 520) responsive to positioning of the button in an unlocked position; characterized in that, in the unlocked position, a blocking tab (250, 450, 550) of the unlocking assembly (240, 400, 440, 540) is moved to create clearance for the flange (130, 226, 426, 526) to contact the piston (232, 432); wherein, in the locked position, the blocking tab (250, 450, 550) is moved to align with the flange (130, 226, 426, 526) and prevent the flange (130, 226, 426, 526) from contacting the piston (232, 432). a jaw assembly (110, 111, 113, 115, 117) configured to extend around a portion of an object through which a fastener is to be driven; a lever (120, 220, 420, 520) configured to be actuated to initiate rivet driving, the lever (120, 220, 420, 520) comprising an operator portion (222, 422, 522), a lever arm (224, 424) and a flange (130, 226, 426, 526), the operator portion (222, 422, 522) being disposed at a front end of the lever arm (224, 424) and the flange (130, 226, 426, 526) being disposed at a rear end of the lever arm (224, 424), wherein, when the lever (120, 220, 420, 520) is actuated via the operator portion (222, 422, 522), the lever arm (224, 424) rotates to rotate the flange (130, 226, 426, 526); a valve assembly portion (230, 330, 430) comprising a piston (232, 432) configured to enable progressive control of rivet driving responsive to actuation of the lever (120, 220, 420, 520); and an unlocking assembly (240, 400, 440, 540) configured to selectively inhibit operation of the lever (120, 220, 420, 520) responsive to positioning of a button of the unlocking assembly (240, 400, 440, 540) in a locked position, and enable operation of the lever (120, 220, 420, 520) responsive to positioning of the button in an unlocked position; characterized in that, in the unlocked position, a blocking tab (250, 450, 550) of the unlocking assembly (240, 400, 440, 540) is moved to create clearance for the flange (130, 226, 426, 526) to contact the piston (232, 432); wherein, in the locked position, the blocking tab (250, 450, 550) is moved to align with the flange (130, 226, 426, 526) and prevent the flange (130, 226, 426, 526) from contacting the piston (232, 432).