An insulating glazing unit including at least two glass sheets spaced apart by a gas-filled cavity, an insert that serves to keep the two glass sheets apart and that has an internal face facing the gas-filled cavity and an opposed external face, and a sealing with respect to the inside of the glazing unit. The insert includes a substantially flat strip that surrounds a first part of the perimeter of the glazing unit, being pressed by its internal face against the edges of the glass sheets and kept fastened by a fastener, and another strip that surrounds a second part of the perimeter of the glazing unit.