Abstract Helong is an Austronesian language spoken in Indonesia with three dialects: Pulau, Bolok and Funai. Helong Pulau has 17 possible vowel sequences and a simple phoneme inventory of fourteen consonants and five vowels. The glottal stop /ʔ/ has a limited distribution, primarily occuring in word-final codas. Several morphophonemic changes, including metathesis, indicate that /ʔ/ is like other consonants. There is also a morphophonological process where the nominalizing prefix /h-/, a voiceless glottal fricative, causes a number of consonants to assimilate to the voiceless phonation of the preceding consonant, seen in muki ‘have (v.)’ → /hm/ [m̥ ] m̥ uki ‘wealth (n.)’, and spirantization as seen in kokon ‘sweep (v.)’ → /hk/ [χ] χokon ‘broom (n.)’. The /h-/ prefix has no assimilatory influence when it precedes voiced stops, as seen in ˈbutu ‘tie (v.)’ → ˈhbutu ‘bundle (n.)’,