A compressed air nailer comprises a working piston connected to a driving tappet configured to drive a fastener. A trigger and a placing sensor are configured to be actuated to aerate or deaerate a main control line to enable triggering of the driving process. A control valve assembly is configured to define a locked position and an open position by controlling a first pressure in a first control space and a second pressure in a second control space. The first control space is connected to the trigger valve and actuation of the trigger valve is configured to bring the safety valve assembly into the locked position. When the safety valve assembly is in the open position, an actuation of the placing sensor valve is configured to bring the safety valve assembly into the open position when the trigger valve is actuated.