Nuclear modification factor ($R_{\text{pA}}$) of isolated prompt photon production in p--Pb collisions at $\snn=5.02$ and \SI{8.16}{TeV}. For illustration purposes, the data points at $\sqrt{s_{\text{NN}}}=\SI{5.02}{TeV}$ are displaced by $\Delta p_{\rm T}=+\SI{300}{MeV}/c$. Vertical bars and boxes denote the statistical and systematic uncertainties, respectively. Coloured boxes around unity denote the respective normalisation uncertainties. The measurement is compared to pQCD calculations using recent (n)PDFs, where the shaded band denotes the nPDF uncertainties. The nPDF uncertainties of the prediction at $\snn=5.02$ coincide with those at \SI{8.16}{TeV} and are therefore omitted for visibility. Theoretical scale uncertainties are fully correlated between both collision systems and are therefore not shown. For improved visibility, the right panel shows only the $R_{\text{pA}}$ at $\sqrt{s_{\text{NN}}}=\SI{8.16}{TeV}$ compared to pQCD calculations at NLO using the nNNPDF3.0~ and nCTEQ15HQ~ nPDFs.