The H.E.S.S. collaboration found several so far unidentified sources ofTeV-gamma-radiation without any known counterpart in other wavelengths. One of those is HESS J1303-631 which was serendipitiously found in thesame field of view of PSR B1259-63 / SS 2883. The possibility that HESSJ1303-631 is a clump of dark matter is discussed.