Accurate density measurements on a binary (hydrogen + carbon dioxide) mixture with a hydrogen mole fraction of 0.05362 were carried out at temperatures T = (273.15, 293.15, and 323.15) K with pressures up to the dew-point pressure or 6.0 MPa, whichever was lower. The gas mixture was prepared gravimetrically. A well-proven two-sinker magnetic suspension densimeter was utilized for the measurements, and a preheating device for the gas sample was specially designed and integrated in order to avoid condensation when filling and flushing the densimeter. Considering all measurement uncertainties in temperature, pressure, density, and composition, the combined expanded uncertainty (k = 2) in density was estimated to be less than or equal to 7.4 × 10-4ρ. The relative deviations of the experimental densities from the GERG-2008 equation of state were less than 0.4%, which is clearly within the uncertainty of this equation. Sorption effects were carefully investigated, and a large impact on the reproducibility of the density measurements on the order of 6 × 10-4ρ (k = 2) was observed. Values and uncertainties of the second and third virial coefficients were determined by fitting a third-order virial equation to the experimental results. The second interaction virial coefficient was determined as well.