The coupling assembly comprises an endpiece suitable for being secured to the outlet of a fluid-flow circuit, and a coupling member comprising a body, at least one housing for receiving said locking balls, a slider defining an axial wall of the housing, a control member provided with a ball-locking element that is movable between an active position in which it entrains the slider into its advanced position, and a release position, and return means for returning the control member into its released position, which return means are interposed between facing walls belonging respectively to the body and to the control member.