A dispensing unit for dispensing a fluid product includes a reservoir for packaging the product, that has a body surmounted by a neck defining an upper opening, a system for dispensing the product, and a device for fixing the dispensing system to the reservoir. The fixing device consists of one single part having securing means on the neck of the reservoir actuated by an axial translational movement and disconnection means with respect to the neck of the reservoir actuated by a rotational movement