The k-Hf9Mo4SiD16.8 deuteride was prepared by deuteration of the intermetallic alloy at room temperature and 0.1 MPa D2 pressure. Synchrotron X-ray and neutron powder diffraction studies revealed that the initial crystal structure is preserved upon deuterium absorption (sp.gr. P63/mmc, a = 8.9553(1) Å, c = 9.0947(2), ∆a/a = 4.0%; ∆c/c = 5.5%; ∆V/V = 14.1%; ∆V/at.D = 2.33 Å3). Deuterium atoms occupy four interstitial positions: two tetrahedral Hf2Mo2 and Hf3Si sites and two triangular Hf3 sites.