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Abstract Precision electroweak tests are a powerful probe of physics beyond the Standard Model, but the sensitivity is limited by the precision with which the W boson mass ($$M_W$$ MW ) has been measured. The Parton Distribution Function (PDF) uncertainties are a potential limitation for measurements of $$M_W$$ MW with LHC data. It has recently been pointed out that, thanks to LHCb’s unique forward rapidity acceptance, a new measurement of $$M_W$$ MW by LHCb can improve this situation. Here we report on a detailed study on the mechanism driving the PDF uncertainty in the LHCb measurement of $$M_W$$ MW , and propose an approach which should reduce this uncertainty by roughly a factor of two using LHCb Run 2 data.