  In a recent paper EPJC 79:187 the general relativistic framework of the
Sagnac effect was investigated. We have some comments on this paper. We show
that their conclusion about the apparent variation of the speed of light does
not hold in stationary spacetimes. Also, We show that their definition of
gravitational Coriolis potential and gravitational Coriolis time dilation are
inconsistent with what is stated in standard references.
