Hawu, an Austronesian language spoken in the Lesser Sunda islands of Indonesia, shows a historical change in which the vowels of adjacent syllables appear to have metathesized. So far as is known, this is the first case of regular vowel metathesis ever reported. Apart from its regularity, what is most striking about this innovation is that it occurred only if V1 was higher (less sonorous) than V2, and if the vowels were separated by a consonant. A fourth noteworthy feature is that the left-dislocated vowel invariably weakened to schwa, whereas similar vowels that remain in situ in either syllable were unaffected. No clear motivation for this change is apparent, and attempts to explain it as something other than direct segmental transposition have so far not met with success.