  Based on an exact formalism, we study the effects of
isospin-symmetry-breaking interactions on superallowed 0+ -> 0+ transitions. We
calculate the second-order renormalization of the Fermi matrix element due to
radial contributions and show that radial excitations neglected in the
treatment of Towner and Hardy are significant. These are estimated to decrease
the isospin-symmetry-breaking corrections. Our results provide a correction
term that can be included in existing approaches.
