Aliovalent doping of solid electrolytes with the intention of increase the concentration of chargecarrying mobile defects is a common strategy for enhancing their ionic conductivities. For the antiperovskite lithium-ion solid electrolyte Li 3 OCl, both supervalent (donor) and subvalent (acceptor) doping schemes have previously been proposed. The effectiveness of these doping schemes depends on two conditions: first, that aliovalent doping promotes the formation of mobile lithium vacancies or interstitials rather than competing immobile defects; and second, that any increase in lithium defect concentration gives a corresponding increase in ionic conductivity. To evaluate the effectiveness of aliovalent doping in Li 3 OCl, we have performed a hybrid density-functional theory study of the defect chemistry of Li 3 OCl and the response to supervalent and subvalent doping. In nominally stoichiometric Li 3 OCl the dominant native defects are predicted to be VLi, O Cl , and V Cl . Supervalent doping increases VLi and O Cl concentrations, with the preferentially-formed defect species dependent on synthesis conditions. Subvalent doping increases the concentration of V Cl more than the concentration of Lii under all accessible synthesis conditions. While supervalent doping is predicted to be effective at increasing ionic conductivity, particularly under Li-poor synthesis conditions, subvalent doping is predicted to decrease room-temperature ionic conductivities at low-to-moderate doping levels. This effect is due to a reduction in the number of lithium vacancies formed during synthesis, and increased V Li + Li i Frenkel-pair recombination upon cooling to room temperature. The strongly asymmetric doping response of Li 3 OCl with respect to supervalent versus subvalent doping is explained as a consequence of the low [VLi + V Cl ] Schottky pair formation energy, suggesting analogous behaviour should be expected in other Schottky-disordered solid electrolytes.