Nuclear modification factor $R_{pA}$ of isolated prompt photon production in p--Pb collisions at 8.16  TeV. The pp reference is obtained through extrapolation from 8 TeV to 8.16 TeV, which was obtained using the JETPHOX program at NLO and included the rapidity boost. The measurement is compared to an existing ATLAS measurement, where the reference is given in the legend. The $R_{pA}$ is compared to various JETPHOX calculations at NLO using different nuclear PDFs and the BFGII fragmentation function. The shaded band denotes the nPDF uncertainty, which has been obtained at 90% CL following LHAPDF guidelines.