  In an earlier paper [1] (hep-ph/0408006), the bound on the Standard Model
Extension photon-sector parameter $\tilde{\kappa}_{tr}$ [2] (hep-ph/0205211)
set by the heavy-ion storage-ring experiment of Saathoff et al. [3] was
incorrectly reported. We show that the correct bound on $\tilde{\kappa}_{tr}$
which resulted from this experiment is in fact $2.2\times 10^{-7}$.
