A dispensing mechanism for an aerosol-generating article, comprising: - an expandable buffering reservoir with an inlet and an outlet; - a dispensing reservoir of constant volume with an inlet and an outlet; - an inlet valve connected to the inlet of the expandable buffering reservoir, wherein the inlet valve is configured to be connected to a liquid storage portion filled with pressurized liquid such that the liquid can only flow from the liquid storage portion to the expandable buffering reservoir; - an outlet valve connecting the outlet of the expandable buffering reservoir to the inlet of the dispensing reservoir such that liquid can only flow from the expandable buffering reservoir to the dispensing reservoir; and - a volume modifier configured to modify the volume of the expandable buffering reservoir; wherein expanding a current volume of the expandable buffering reservoir to an expanded volume causes a drawing of liquid from the cartridge to the expandable buffering reservoir until the expanded volume of the expandable buffering reservoir is filled up with the liquid; wherein compressing the expanded volume of the expandable buffering reservoir causes an expelling of liquid from the expandable buffering reservoir to the dispensing reservoir until the dispensing reservoir is filled up with the liquid; wherein the dispensing reservoir is configured to release its content of liquid during one puff of a user; wherein the volume modifier comprises a piston that is configured to define, together with a housing in which the dispensing mechanism is arranged, a moving chamber, wherein the expandable buffering reservoir is coupled to one side of the piston and arranged in the moving chamber such that moving the piston longitudinally relative to the housing causes modifying the volume of the expandable buffering reservoir; and wherein the dispensing reservoir is coupled to the other side of the piston opposite to the moving chamber, thereby causing the dispensing reservoir to be moved together with the piston longitudinally in the housing. - an expandable buffering reservoir with an inlet and an outlet; - a dispensing reservoir of constant volume with an inlet and an outlet; - an inlet valve connected to the inlet of the expandable buffering reservoir, wherein the inlet valve is configured to be connected to a liquid storage portion filled with pressurized liquid such that the liquid can only flow from the liquid storage portion to the expandable buffering reservoir; - an outlet valve connecting the outlet of the expandable buffering reservoir to the inlet of the dispensing reservoir such that liquid can only flow from the expandable buffering reservoir to the dispensing reservoir; and - a volume modifier configured to modify the volume of the expandable buffering reservoir; wherein expanding a current volume of the expandable buffering reservoir to an expanded volume causes a drawing of liquid from the cartridge to the expandable buffering reservoir until the expanded volume of the expandable buffering reservoir is filled up with the liquid; wherein compressing the expanded volume of the expandable buffering reservoir causes an expelling of liquid from the expandable buffering reservoir to the dispensing reservoir until the dispensing reservoir is filled up with the liquid; wherein the dispensing reservoir is configured to release its content of liquid during one puff of a user; wherein the volume modifier comprises a piston that is configured to define, together with a housing in which the dispensing mechanism is arranged, a moving chamber, wherein the expandable buffering reservoir is coupled to one side of the piston and arranged in the moving chamber such that moving the piston longitudinally relative to the housing causes modifying the volume of the expandable buffering reservoir; and wherein the dispensing reservoir is coupled to the other side of the piston opposite to the moving chamber, thereby causing the dispensing reservoir to be moved together with the piston longitudinally in the housing.