Comment on `Six-state clock model on the square lattice: Fisher zero approach with Wang-Landau sampling'

Hwang in [Phys. Rev. E 80, 042103 (2009)] suggested that the two transitions of the six-state clock model on the square lattice are not of the Kosterlitz-Thouless type. Here we show from simulations thatat the upper transition, the helicity modulus does make a discontinuous jump to zero. This gives strong evidence for a Kosterlitz-Thouless transition.