After the preparation of this manuscript and before sending it for publication, our attention has been drawn to an article about the oxygen release and incorporation in BaFeO3 polymorphs (Watanabe et al, February 18, 2024) . A fully oxygenated 6H-BaFeO3 sample has been prepared by using high-pressure (8 GPa) and high-temperature (1000 ºC) conditions with KClO4 as oxidizing agent. These authors have described that sample 6H loses weight when heated in air up to 600 ºC, obtaining a composition close to BaFeO2.8. The temperature-dependent synchrotron X-ray diffraction in situ shows that the 6H-type are essentially the same keeping the P63/mmc hexagonal symmetry from room temperature to 600 ºC.