A capacitor fastening for fastening a capacitor to a panel, whereby the capacitor, when mounted in place, is positioned in the panel, fastened at its lower part. The capacitor fastening includes a retainer in the panel at the mounting point of the capacitor for preventing lateral movement of the capacitor in at least one selected direction; a tightening plate arranged above the panel and to be fastened to the panel, which tightening plate has a hole substantially corresponding to the diameter of the capacitor above the mounting point of the panel; and a wedge between the panel and the tightening plate for tightening the retainer of the panel and the edge of the hole in the tightening plate from opposite directions against the capacitor.