  The radiative corrections to double-Dalitz
($P\to\bar{\ell}\ell\bar{\ell'}\ell'$) decays are revisited and completed up to
next-to-leading order in QED, finding mild differences with respect to previous
studies. These might be relevant for extracting information about the mesons
transition form factors, which play an important role in determining the
hadronic light-by-light contribution to the anomalous magnetic moment of the
muon.
