Malay (Rumi) is alphabetic and has a transparent, agglutinative system of affixation. We manipulated language-specific junctural phonetics in Malay and English to investigate whether morphophonemic L1-knowledge influences L2-processing. A morpheme decision task, "Does this "nonword" sound like a mono- or bi-morphemic English word?", was developed by crossing English Transitional Probability (high vs. low) with Malay Transitional Possibility (possible vs. impossible). The data for Malay-L1/English-L2 adults (N = 21) provide clear and reliable empirical evidence of L1-to-L2 morphophonemic transfer: Participants were more accurate at identifying transitional boundaries in English when they are also possible in Malay. Pedagogical implications are discussed.