In a foundation for a windmill with a circular or polygonal pedestal for supporting a windmill tower and a plurality of ribs, which project radially outwards from the pedestal, the pedestal is divided into a plurality of circumferential portions, wherein a circumferential portion and a rib are each formed by at least one prefabricated concrete element, respectively, and wherein the prefabricated concrete elements are made of reinforced concrete, which includes a first reinforcement structure, which includes radial tensioning elements, in particular tension rods or tensioning strands, for stressing the prefabricated concrete elements. A second reinforcement structure is also provided, which holds the circumferential portions together and is coupled with the first reinforcement structure, in particular the radial tensioning elements.