A filler coupling comprising an isolation valve that can move relative to a seat between an upstream closing position and a downstream opening position, said isolation valve being moved to its upstream position by a return member, the coupling also comprising a dust-prevention valve placed upstream of the isolation valve, said dust-prevention valve comprising a downstream end and being able to move relative to the body between an upstream closing position and a downstream opening position, said dust-prevention valve being moved to its upstream position by a return member, characterized in that the dust-prevention valve can be moved selectively downstream either: in a first determined downstream position opening the upstream end in which the downstream end of the dust-prevention valve does not push the upstream end of the isolation valve, or in a second determined downstream position opening the upstream end, in which the downstream end of the dust-prevention valve pushes an upstream end of the movable isolation valve in order to move the isolation valve by contact to its downstream open position, and in that the dust-prevention valve comprises one or more passageways for guiding at least a portion of the fluid stream traveling from upstream to downstream through the body of said dust-prevention valve.