  In this work, we revisit the model of PbTe presented in [E. Fradkin, E.
Dagotto, and D. Boyanovsky, Phys. Rev. Lett. 57, 2967 (1986)]. We show that the
low energy theory of this model corresponds to a (higher-order) topological
crystalline insulator in space group $Fm\bar{3}m1'$, diagnosable by symmetry
indicators. We show that the gapless fermions found on antiphase domain walls
are the topological boundary modes of the system, due to a nonvanishing mirror
Chern number. Furthermore, we show that any symmetric completion of the model
must be in this same topological phase. Finally, we comment on the relationship
of this model to realistic PbTe, which has recently been predicted to have a
phase which realizes same bulk symmetry indicators.
