  Adding a hard photon to the final state of a leptonic pseudoscalar-meson
decay lifts the helicity suppression and can provide sensitivity to a larger
set of operators in the weak effective Hamiltonian. Furthermore, radiative
leptonic $B$ decays at high photon energy are well suited to constrain the
first inverse moment of the $B$-meson light-cone distribution amplitude, an
important parameter in the theory of nonleptonic $B$ decays. We demonstrate
that the calculation of radiative leptonic decays is possible using Euclidean
lattice QCD, and present preliminary numerical results for $D_s^+ \to \ell^+
\nu\gamma$ and $K^- \to \ell^-\bar{\nu}\gamma$.
