  We revisit the recent limits from LHCb on a Majorana neutrino N in the mass
range 250 - 5000 MeV. These limits are among the best currently available, and
they will be improved soon by the addition of data from Run 2 of the LHC. LHCb
presented a model-independent constraint on the rate of like-sign leptonic
decays, and then derived a constraint on the mixing angle V{\mu}4 based on a
theoretical model for the B decay width to N and the N lifetime. The model used
is unfortunately unsound. We revise the conclusions of the paper based on a
decay model similar to the one used for the tau lepton and provide formulae
useful for future analyses.
