Clumped isotope thermometry can independently constrain the formation temperatures of carbonates, but a lack of precisely temperature-controlled calibration samples limits its application on aragonites. To address this issue, we present clumped isotope compositions of aragonitic bivalve shells grown under highly controlled temperatures (1‒18 deg C), which we combine with clumped isotope data from aragonites precipitated in a wide range of temperatures (1‒850 deg C). We observe no offset in clumped isotope values between aragonitic foraminifera, mollusks, and abiogenic aragonites or between aragonites and calcites, eliminating the need for need for a mineral-specific calibration or acid fractionation factor. However, due to non-linear behavior of the clumped isotope thermometer, including high-temperature (>100 deg C) datapoints in linear clumped isotope calibrations causes them to underestimate temperatures of cold (1‒18 deg C) carbonates by 2.7 +/- 2.0 deg C (95% confidence level). Therefore, clumped isotope-based paleoclimate reconstructions should be calibrated using samples with well constrained formation temperatures close to those of the samples.