Lax (also known as, centralized) vowel allophones are attested in Indonesian for non‐low vowels in closed syllables [e.g., Sneddon (1996)]. In consonant‐final stems with vowel‐initial suffixes (ke+apik+an), phonological theory (the maximal onset principle) predicts the stem‐final consonant to syllabify with the suffix (ke.a.pi.kan) and the preceding vowel to manifest as unreduced. This study compares speaker‐normalized formant values for such vowels against formant values for vowels in stem‐final open syllables with obstruent‐initial affixes (men+jadi+kan) and vowels in monomorphemic contexts (tikam). Word‐final open and closed syllables (jadi, cerdik) are included as reference points in the vowel space. Male and female L1 speakers of standard Indonesian are recorded reading three randomizations of the word list. Data collection is ongoing, but preliminary results suggest that for front (unround) vowels in stem‐final closed syllables with vowel‐initial affixes (ke+apik+an), the formant values fall between the values for prototypical lax and non‐lax Indonesian vowels; no clear pattern has yet emerged for back (round) vowels. Findings suggest that morphological structure (i.e., whether a segment “belongs” to stem or affix) may constrain syllabification or cause deviations from preferred syllable structures.