A diaphragm pump including, in a pump body, a hydraulic control chamber disposed between a piston for executing reciprocating motion and the diaphragm, the pump including elements for compensating leaks from the hydraulic chamber, the elements including a refilling duct opening out into the hydraulic chamber via a normally-closed compensation shutter that is driven into the open position by the diaphragm, wherein the above-mentioned compensation shutter being driven by the diaphragm pressing against a free end of a rod for controlling the shutter, the diaphragm being subjected to the force of a suction-assistance spring which co-operates with the above-mentioned shutter to return it to its closed position by pushing the free end of the control rod back towards the diaphragm, the spring co-operating with the shutter to form a moving assembly that is moved without being deformed by the diaphragm during suction overtravel.