  Recently, Kristensen, Ge and Hughes have compared [Phys. Rev. A 92, 053810
(2015)] three different methods for normalization of quasinormal modes in open
optical systems, and concluded that they all provide the same result. We show
here that this conclusion is incorrect and illustrate that the normalization of
[Opt. Lett. 37, 1649 (2012)] is divergent for any optical mode having a finite
quality factor, and that the Silver-Mueller radiation condition is not
fulfilled for quasinormal modes.
