An air filter system, in particular for the intake air of internal combustion engines, is provided. It comprises a housing with a housing upper part and a round air filter element for filtering air, the housing comprising a clean air connection for discharging clean air from the housing and an annular sealing groove axially opened towards the interior area of the housing surrounding the clean air connection for the engagement of an annular sealing web axially extending away from the filter element, the sealing groove featuring a cylindrical contact area to which a sealing surface of the sealing web can be applied in particular radially sealingly, wherein the sealing groove features a cylindrical support area facing the contact area and the support area features at least one extension protruding from the support area in the direction of the sealing surface, wherein the sealing web features a second surface opposite to the sealing surface that features several annularly surrounding indentations in radial direction, wherein the at least one extension engages respectively one of the indentations.