This study examines monolingual and multilingual individuals’ discrimination of stop consonants in a language to which they had never been exposed: Korean. If bilingualism leads to increased flexibility in phonological categorization, we may see a broad-based bilingual advantage for phoneme discrimination. Using a Korean phoneme discrimination task, we compared 56 adults in four groups: monolingual English, bilingual Spanish, bilingual Armenian, and trilingual. Findings indicate that Spanish–English bilingual individuals scored no better than English monolinguals, and lower than Armenian–English bilingual individuals. In this case, the advantage from early childhood non-English exposure or current bilingualism was found to be specific only to languages with similar phonemic categories. This supports a narrow first/second language to third language transfer view of phoneme discrimination skills.