Gauged supergravity from dimensional reduction

We perform a generalised Scherk-Schwarz reduction of the effective action of the heterotic string on T6 to obtain a massive N = 4 supergravity theory in four dimensions. The local symmetry-group of the resulting d = 4 theory includes a Heisenberg group, which is a subgroup of the global O(6,6 + n) obtained in the standard reduction. We show explicitly that the same theory can be obtained by gauging this Heisenberg group in d = 4, N = 4 supergravity.