A fastening unit for connecting a heat-generating body to a heat sink is provided. The fastening unit includes a retaining pin and a retaining element wherein the retaining pin is connected to a retaining head. The retaining pin extends through the retaining element and the retaining head contacts the retaining element. The retaining element is engageable upon a body of the heat sink so as to retain same in a fastening direction of the retaining pin. The retaining element is engageable laterally on the body of the heat sink, the retaining element having, on a side thereof for facing the body of the heat sink, a retaining groove extending in a longitudinal direction perpendicular to the fastening direction. In an assembled state for the fastening unit, at least one groove surface of the retaining groove of the retaining element contacts the body of the heat sink.