Doping control is necessary to unlock the scientific and technological potential of many materials, including ternary II-IV-nitride semiconductors, which are closely related to binary GaN. In particular, ZnSnN2 has been reported to have degenerate doping density, despite bandgap energies that are well suited for solar energy conversion. Here, we show that annealing Zn-rich Zn1+xSn1-xN2 grown with added hydrogen reduces its free electron density by orders of magnitude, down to 4 x 1016 cm-3. This experimental observation can be explained by hydrogen passivation of acceptors in Zn1+xSn1-xN2 during growth, lowering the driving force for unintentional donor formation. Lastly, these results indicate that the doping control principles used in GaN can be translated to ZnSnN2, suggesting that other strategies used in binary III-Vs can be applied to accelerate the technological development of ternary II-IV-N2 materials.