A coupler for a backhoe or other excavator includes a frame with a lock system including a first safety lock that moves relative to a first hook between an engaged position for capturing the first associated attachment pin in the first hook and a disengaged position for releasing the first associated attachment pin from the first hook. An actuator moves the first safety lock between its engaged and disengaged positions. At least a first lock arm is movable between a locked position and an unlocked position. The first lock arm engages and retains the first safety lock in its engaged position when the first lock arm is in its locked position. The first lock arm is movable to its unlocked position by contact with the associated backhoe or excavator arm when the frame is moved to a curled position relative to the associated backhoe or excavator arm.