This is an addendum to the authors’ previous paper in which criteria for cuspidal
edges and swallowtails on surfaces are given by applying the so-called Zakalyukin’s
lemma. The original statement in Zakalyukin’s paper assumed the properness of the
mappings. However, the lemma in the appendix of our paper did not assume
properness. Recently, we noticed that the proof given in the appendix was implicitly
relying on properness. In this addendum, we prove that mappings satisfying the
criteria of cuspidal edges and swallowtails have properness. Consequently, the criteria
are clarified.