  A search for $\Sigma^+ \to p \mu^+ \mu^-$ decays with LHCb Run 1 data is
presented, yielding an evidence for this decay and a measurement of a branching
fraction compatible with the Standard Model. The HyperCP anomaly in the dimuon
invariant mass distribution is not confirmed, and its branching fraction
central value is excluded at 95\% CL. Prospects for the future of this
measurement in LHCb are also presented.
