The ratio of branching fractions of Bc+→Bs0π+ and Bc+→J/ψπ+ decays is measured with proton-proton collision data of a centre-of-mass energy of 13 TeV. The data were collected with the LHCb experiment during 2016–2018, corresponding to an integrated luminosity of 5.4 fb−1. The Bs0​ mesons are reconstructed via the decays Bs0→J/ψϕ and Bs0→Ds−π+. The ratio of branching fractions is measured to be B(Bc+→Bs0π+)/B(Bc+→J/ψπ+)=91±10±8±3 where the first uncertainty is statistical, the second is systematic and the third is due to the knowledge of the branching fractions of the intermediate state decays. [graphic not available: see fulltext]