The defect structure of gamma-Bi2V0.9Ni0.1O5.35 (BINIVOX, x = 0.10) quenched from high temperature has been refined using X-ray and neutron powder diffraction data. The defect structure shows that oxide ion vacancies are exclusive to the equatorial positions around the Ni/V atom. Consideration of site occupancies, inter-site contact distances, and geometrical constraints yields two likely coordination environments for V/Ni, i.e. distorted tetrahedral and distorted octahedral. The percentage of V/Ni sites that are distorted tetrahedra may be calculated as 68% with the remainder as distorted octahedra.