Abstract: A sealing device (2, 2?, 2?) to be arranged between an opening in a drinking container (1?, 1?) and a drinking straw (20), and a method of making the sealing device (2, 2?, 2?). The sealing device (2, 2?, 2?) comprises a region of the drinking container (1?, 1?), or a part connected to the drinking container (1?, 1?), made from a material (14) subjected to a plastic deformation in a portion spanning said opening in the drinking container (1?, 1?). The deformation has the form of a bulge (2a) of thinned material (4). The bulge (2a) is folded upon itself to form a ring-shaped fold (12) on the inside of the drinking container (1?, 1?). The fold (12) encircles the plastically deformed and thinned wall material (4) of bulge (2a), said bulge material (4) forming an inner seal ring (19) around the drinking straw (20) when the bulge material (4) is perforated.