In a method an inner segment is first pre-assembled on each of a number of outer segments by at least one fixing element, so as to produce a plurality of segment modules having each a predetermined air gap between the inner segment and the outer segment. The inner segments and the outer segments are assigned to the rotor or stator of the electrical machine. The inner segments of the plurality of segment modules are fastened to an inner assembly device (for example a hub). The outer segments of the plurality of segment modules are fastened to an outer assembly device (for example a supporting structure). Finally, the fixing elements between the inner segments and the outer segments are removed.