A filter system for filtering a fluid has a filter housing with a housing top part and a housing bottom part, wherein the housing top part and the housing bottom part extend along a housing axis. An outlet socket is arranged at the housing top part and is provided to discharge the fluid after having been filtered. A non-return valve is arranged in an interior of the outlet socket. A filter element is arranged in the filter housing and separates a raw fluid side and a clean fluid side from each other. The filter element has a valve seat interacting with the non-return valve. The non-return valve closes in a closed position of the non-return valve a fluid path through the outlet socket and opens in an open position of the non-return valve the fluid path through the outlet socket.