Elastic properties of leucite have been investigated using resonant ultrasound spectroscopy over a temperature range from 300 to 1400 K. According to these measurements, elastic moduli soften by ~50% at the Ia 3 d-I 41/ acd ferroelastic transition temperature T c1 = 940 K relative to the value at 1400 K. A second softening is observed at T c2 = 920 K, corresponding to the structural change from the space group I 41/ acd to I 41/ a . These elastic anomalies are analyzed in a simple model under the assumption that the transitions observed at T c1 and T c2 can be approximated by a single pseudoproper ferroelastic transition. The two phase transitions are accompanied by a single peak in mechanical damping attributed to the high mobility of twin walls in the intermediate phase followed by pinning in the low-temperature phase. To determine whether twin walls in tetragonal leucite are polar, resonant piezoelectric spectroscopy and second harmonic generation measurements were performed, but no evidence of polarity was found.