The invention relates to a fuel cell system comprising a fuel cell stack (2) received in a first housing (1) and an energy supply unit received in a second housing (3), the two housings (1, 3) being connected or being capable of being connected in such a manner that openings (4, 5) provided in the housings (1, 3) are opposite one another and overlap, at least in part. According to the invention, an insert (6), which surrounds a pin or sleeve-shaped contact element (7) is arranged in the area of two opposing and at least in part overlapping openings (4, 5), wherein the insert (6) directly, or indirectly via a sealing ring (8), encloses the contact element (7) in a watertight manner and isolates same electrically at least against one of the two housings (1, 3).