  We evaluate the impact of radiative corrections in the ratios $\Gamma[B\to M
\mu^+\mu^-]/\Gamma[B\to M e^+e^-]$ when the meson $M$ is a $K$ or a $K^*$.
Employing the cuts on $m^2_{\ell\ell}$ and the reconstructed $B$-meson mass
presently applied by the LHCb Collaboration, such corrections do not exceed a
few $\%$. Moreover, their effect is well described (and corrected for) by
existing Montecarlo codes. Our analysis reinforces the interest of these
observables as clean probe of physics beyond the Standard Model.
