A device for gas filling a duct intended to be filled with gas and positioned in a container of a collapsible type, said duct being defined by two opposite side walls, which are joined along a common connecting portion, and comprising an inlet arranged through one of the side walls, the device comprising:
- an abutment;
- and
- a gas module which is axially applicable to the abutment for abutment against a part of the container and the inlet arranged therein, the gas module being arranged to fill the duct with gas through the inlet,
- wherein the abutment includes a recess formed in a side of the abutment that is facing the container for allowing a portion of at least one side wall forming the duct to bulge during the filling of the duct with gas in order to form a free passage into the duct.