When left in air, as‐grown anodic oxides grown under optimized conditions described in the literature have been found to age. It is shown that this is caused by a hygroscopic component in the outer indium‐rich layer of the oxide film. When oxalic acid is present in the forming electrolyte, this phenomenon is not observed: As‐grown oxides are stable and have a constant composition throughout their thickness. This paper discusses some of the properties of the oxide films, both as‐grown and annealed, and some aspects of the chemistry of their formation. This distinct behavior of oxalic acid can be attributed to the fact that it forms soluble complexes with In(III) in the relevantpH range.