The extended main-sequence turn-offs (eMSTOs) and extended red clumps (eRCs) observed in intermediate-age star clusters challenge the traditional understanding of star clusters as simple stellar populations. In recent years, eMSTOs have been interpreted as signatures of fast stellar rotation, but the role of rotational mixing in shaping the colour–magnitude diagram (CMD) of these clusters remain uncertain. I will present a comparison between observed and synthetic CMDs for two intermediate-age clusters, NGC 419 and NGC 1817. Both clusters show a clear eMSTO and eRC, with turn-off stars showing large v sin i values. We used two grids of rotating stellar models, identical in input physics except for the efficiency of rotational mixing, to build synthetic clusters. Our results show that models with weak rotational mixing best reproduce both the eMSTO and eRC features and match the red clump luminosities and asteroseismic masses in NGC 1817. Strong mixing leads to post main-sequence CMD features that are too bright and inconsistent with observations. Overall, our findings suggest that rotational mixing might play a role in shaping eRCs, but its influence on intermediate-mass stellar evolution is definitely weaker than most stellar models predict.