  We consider the family of singularity-free rotating black hole solutions in
Einstein's conformal gravity found in Bambi, Modesto & Rachwal (2017) and we
constrain the value of the conformal parameter $L$ from the analysis of a 30 ks
NuSTAR observation of the stellar-mass black hole in GS 1354-645 during its
outburst in 2015. Our new constraint is much stronger than that found in
previous work. Here we obtain $L/M < 0.12$ (99% confidence level, statistical
uncertainty only).
