The c. 2.06 Ga Bushveld Complex intrudes the Transvaal Supergroup, South Africa. Calcsilicate xenoliths within the mafic phase of the Bushveld Complex (Rustenburg Layered Suite, or RLS) preserve calcsilicate xenoliths with high-temperature (c. 1200°C) mineralogies that were later metasomatized by hydrous, retrograde (c. 600–700°C) fluids whose timing has been unconstrained. New U–Pb isotope data from newly grown titanite within a completely retrogressed xenolith indicates that retrogression occurred at 2058.9±0.8 Ma. This suggests that retrogression was due to hydrothermal circulation associated with the cooling RLS, and not slightly later Bushveld-related granites. The new data place a tight constraint on the minimum age of emplacement of the RLS.