An assembly method for a fluid product dispenser, in particular of the dropper type, comprising: - a reservoir containing fluid product and air, the reservoir forming an assembly opening, - a fluid product dispenser cannula in communication with the reservoir, the dispenser cannula forming a dispenser end that is advantageously suitable for forming a drop of fluid that separates from the dispenser end by gravity, and - an actuator member engaged in the assembly opening, for supplying the dispenser cannula with fluid coming from the reservoir, the actuator member comprising a deformable membrane that defines an outside face forming a pusher, and an inside face that is in contact with the air of the reservoir, when the dispenser cannula is in contact with the fluid of the reservoir, the deformable membrane is movable between a rest position and a fully depressed position so as to define, between these two positions, an actuation volume Va, the actuator member includes an assembly sleeve that is inserted in sealed manner in the assembly opening of the reservoir, the assembly sleeve performs one sealed axial stroke in the assembly opening of the reservoir in order to reach its final sealed assembled position, the sealed axial stroke defining a stroke volume Vc, the actuation volume Va being greater than or preferably substantially equal to the stroke volume Vc of the assembly sleeve, the assembly method comprising the following steps: a - filling the reservoir with fluid via its assembly opening in the absence of the actuator member, b - engaging the actuator member in the assembly opening of the reservoir, the deformable membrane being held in its fully depressed position when the assembly sleeve comes into sealed contact with the assembly opening of the reservoir, and c - while the assembly sleeve is in sealed contact with the assembly opening of the reservoir, releasing the deformable membrane, which thus returns into its rest position. - a reservoir containing fluid product and air, the reservoir forming an assembly opening, - a fluid product dispenser cannula in communication with the reservoir, the dispenser cannula forming a dispenser end that is advantageously suitable for forming a drop of fluid that separates from the dispenser end by gravity, and - an actuator member engaged in the assembly opening, for supplying the dispenser cannula with fluid coming from the reservoir, the actuator member comprising a deformable membrane that defines an outside face forming a pusher, and an inside face that is in contact with the air of the reservoir, when the dispenser cannula is in contact with the fluid of the reservoir, the deformable membrane is movable between a rest position and a fully depressed position so as to define, between these two positions, an actuation volume Va, the actuator member includes an assembly sleeve that is inserted in sealed manner in the assembly opening of the reservoir, the assembly sleeve performs one sealed axial stroke in the assembly opening of the reservoir in order to reach its final sealed assembled position, the sealed axial stroke defining a stroke volume Vc, the actuation volume Va being greater than or preferably substantially equal to the stroke volume Vc of the assembly sleeve, a - filling the reservoir with fluid via its assembly opening in the absence of the actuator member, b - engaging the actuator member in the assembly opening of the reservoir, the deformable membrane being held in its fully depressed position when the assembly sleeve comes into sealed contact with the assembly opening of the reservoir, and c - while the assembly sleeve is in sealed contact with the assembly opening of the reservoir, releasing the deformable membrane, which thus returns into its rest position.