A fluid dispenser having a fluid reservoir (2) for containing fluid, the reservoir including an opening (230) having an outer top edge (25) and an inner bottom edge (26); a dispenser member (3), such as a pump or a valve; a fastener that fastens the dispenser member in the opening (230). The dispenser includes a tamperproofing mechanism (1) that is distinct from the fastener and that is secured to the dispenser member (3). The tamperproofing mechanism comes into contact with the inner edge (26) in the event of an attempt at removing the dispenser member (3) from the opening (230).