Production cross section of $\mu^+\mu^-$ from Z-boson decays, measured in p--Pb collisions at \eightnn and compared with theoretical calculations both based on CT14 (at NLO) free-nucleon PDFs  and on other PDF sets including the presence of a nuclear modification. The horizontal extension of the data points correspond to the measured rapidity range. The bars and boxes correspond to the statistical and systematic uncertainties respectively. The theory points are horizontally shifted for better readability.