The present study investigated segment-based serial planning mechanism during syllabic language (Cantonese) speech planning by Dutch-Cantonese bilinguals. Our results show a behavioral facilitation for phoneme onset sharing in Cantonese, a syllabic language, for Dutch-Cantonese bilinguals. This is in contrast to behavioral results with monolingual Cantonese speakers where segmental onset facilitation is normally absent (Wong and Chen, 2008; Wong et al., 2012). Our finding is probably due to the native proficiency of our participants in Dutch, a segment-based language in which phoneme onset effects are found (Schriefers et al., 1990; Meyer, 1991; Meyer and Schriefers, 1991). Their experience with Dutch facilitates segment production in Cantonese. Thus, our bilinguals seemed to be able to utilize their segment-oriented production strategy used in Germanic languages and apply it to their syllabic language, Cantonese. This is in line with a previous study showing that Mandarin-English bilinguals with a good proficiency in English can demonstrate initial segmental facilitation during reading aloud in Mandarin under specific conditions (e.g., same tonal pattern). However, Ida et al. (2015) were not able to replicate this effect with proficient Japanese-English bilinguals in Japanese. Thus, there is mixed evidence that the unit size of English as a second language can exhibit influence on that of L1 speech processing. The present study is the first to show phoneme onset facilitation in Cantonese speech production for native speakers of a segment-based language. This may suggest that the primary processing unit in a specific language is dependent on the speakers's general language background. Within spoken word recognition bilinguals have also shown to use the unit of lexical access from their dominant language in their second language if it is an efficient processing strategy for that language (Cutler et al., 1989, 1992).