This paper examines the internal evidence for the syllabic affiliation of onglides in Isbukun Bunun, a Formosan language spoken in southern Taiwan. It is shown that although the phonotactics of the onglides and the neighboring elements does not provide crucial evidence for the status of the glides, postconsonantal onglides are structurally closer to the nucleus based on their weight-carrying behavior in stress assignment. The proposed analysis implies that although Isbukun contains prevocalic consonant-glide sequences and postvocalic glide-consonant strings, complex syllable margins are in fact not tolerated in the language.