Embodiments of a compressor cutoff are presented. In an embodiment, the present invention includes apparatus for cutting off the flow of gas/liquid in the event of compressor failure or breakdown. In this embodiment, gas/liquid flows from its source through one or more passageways into a first input chamber, and also through one or more other passageways into a second input chamber, where the first and second input chambers are separated by a stop plunger. During the down-stroke of the compressor's piston, gas/liquid in the first chamber passes (or is drawn) through an inlet valve of the piston bore, and during the up-stroke of the piston that gas/liquid is forced through an outlet valve to a tank or other compressed gas/liquid receptacle. So long as the compressor operates normally, the pressure in the two input chambers (i.e., on each side of the stop plunger) will be substantially equal, thereby keeping the stop plunger in place. If, however, the compressor fails in a manner that exposes gas/liquid in the piston bore to the atmosphere, or otherwise results in a decrease in pressure in the piston bore, the pressure in the first input chamber will fall below the pressure in the second input chamber, thereby causing the stop plunger to move to a position in which it blocks the flow of gas/liquid from entering the inlet valve of the piston bore.