It has always been assumed that CaSnO3 perovskite remains orthorhombic (Pbnm) as a function of temperature up to its melting point, and is rather unremarkable in many ways. However, we have recently found evidence for short range order-disorder from Raman spectroscopy, with a strong first order shift in Raman mode frequencies accompanied by a doubling of the widths of the same Raman lines, on heating through around 430 K. The "transition" is reversible, appearing at around 360 K on cooling. High-temperature X-ray diffraction shows no major discernible transformation at these temperatures, but calorimetry indicates a very small excess heat capacity at similar temperatures. We wish to test the hypothesis that that this is due dynamical disorder, possible short-range in character, and wish to undertake a more precise and definitive set of neutron powder diffraction data as a function of T.