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Integrated X-ray intensities of Bragg peaks have been measured with an NbC0.72 single-crystal which contains a large number of non-stoichiometric carbon vacancies. By standard structural analysis the mean-square displacements were determined to be (u2Nb) = 0.0041 (7) Å2 for Nb atoms and (u2C) = 0.0111 (20) Å2 for C atoms. This (u2Nb) is comparable to the value of 0.0045 Å2, extrapolated from the compositional dependence of (u2Nb) proposed by Metzger, Peisl & Kaufmann [J. Phys. F. (1983). 13, 1103-1113]. It was confirmed that the existence of carbon vacancies induces larger static displacements of neighbouring niobium atoms, and the contribution of thermal displacements to the observed (u2Nb) appears to be rather small in a non-stoichiometric niobium monocarbide.