We report a temperature-dependent high-resolution X-ray diffraction investigation of 200 nm epitaxial BiFeO3 thin films grown on (001) SrTiO3. We were successful in making epitaxial thin films thermally stable, a key requirement for this study. Our results provide evidence that BiFeO3 undergoes three high-temperature transitions: an antiferromagnetic transition at 425°C, a first-order α–β phase transition between 745°C and 780°C and a smoother transition toward the γ-phase at 860°C. Both the α–β and β–γ transitions take place 60°C lower than the bulk values whereas the antiferromagnetic transition occurs 55°C higher. This underscores the part played by strain and also emphasizes that BiFeO3 is not a conventional ferroelectric perovskite. Reciprocal space maps reveal the unusual result that the thin films remain monoclinic on crossing the α–β phase transition. Linear extrapolation of the in-plane lattice parameters to higher temperatures rules out cubic symmetry for the γ-phase.