  The ``magnetic force theorem'' is frequently used to compute exchange
interaction parameters and adiabatic spin-wave spectra of ferromagnets. The
interest of this approach is that it allows to obtain these results from a
non-self-consistent calculation of the (single-electron) band energy only,
which greatly reduces the computational effort. However, as discussed by
various authors, this approach entail some systematic error. Here, a
``renormalized magnetic force theorem'' allowing to remove this systematic
error without increasing significantly the computational effort is presented.
For systems with one atom per unit cell, it amounts to a simple renormalization
of the spin-wave spectrum. This renormalization greatly improves the agreement
between calculated and experimental Curie temperatures of Fe and Ni.
