A measurement of the jet mass distribution in hadronic decays of Lorentz-boosted top quarks is presented. The measurement is performed in the lepton + jets channel of top quark pair production (\documentclass[12pt]{minimal}
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				\begin{document}$$\hbox {t}\overline{\hbox {t}}$$\end{document}tt¯) events, where the lepton is an electron or muon. The products of the hadronic top quark decay are reconstructed using a single large-radius jet with transverse momentum greater than 400\documentclass[12pt]{minimal}
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				\begin{document}$$\,\text {Ge}\hspace{-.08em}\text {V}$$\end{document}GeV. The data were collected with the CMS detector at the LHC in proton-proton collisions and correspond to an integrated luminosity of 138\documentclass[12pt]{minimal}
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				\begin{document}$$\,\text {fb}^{-1}$$\end{document}fb-1. The differential\documentclass[12pt]{minimal}
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				\begin{document}$$\hbox {t}\overline{\hbox {t}}$$\end{document}tt¯production cross section as a function of the jet mass is unfolded to the particle level and is used to extract the top quark mass. The jet mass scale is calibrated using the hadronic W boson decay within the large-radius jet. The uncertainties in the modelling of the final state radiation are reduced by studying angular correlations in the jet substructure. These developments lead to a significant increase in precision, and a top quark mass of\documentclass[12pt]{minimal}
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				\begin{document}$$173.06 \pm 0.84\,\text {Ge}\hspace{-.08em}\text {V} $$\end{document}173.06±0.84GeV.