A diaphragm valve comprises at least one valve body which has at least one inlet, at least one outlet, at least one flow channel and at least one shutoff web dividing the flow channel into channel portions. The diaphragm valve furthermore comprises a diaphragm which rests on a circumferential sealing seat of the valve body, and a drive having a drive housing, the drive being coupled to the diaphragm to press the diaphragm against the shutoff web for closing the valve. The diaphragm valve furthermore comprises a fastening unit for detachably locking the drive to the valve body, the fasting unit having a bayonet cap and an additional central retightening unit by means of which an axial tightening force is generated.