The invention relates to a self-closing seal with a sealing cap (1), a through opening (8) formed in the sealing cap (1) and a sealing membrane (2) associated with the through opening (8). The sealing membrane (2) has a lower mounting edge (3) and an upper sealing cover (5) extending so as to be substantially concave. The sealing cover (5) and the mounting edge (3) are connected by means of a connecting wall (4). To achieve an advantageous solution when in use and for manufacturing purposes, it is proposed to construct an extension area (9) externally adjacent the through opening (8), to arrange the sealing cover (5) in the extension area (9), and to extend the connection wall (4) into the extension area (9) by traversing the through opening.