This study investigates dominant language transfer (from English) in adult Spanish second language (L2) learners and Spanish heritage speakers. We focus on contrasting properties of English and Spanish definite articles with respect to generic reference ("Elephants have ivory tusks" vs. "Los elefantes tienen colmillos de marfil") and inalienable possession ("Peter raised his hand" vs. "Pedro levantola mano"). Thirty adult Spanish heritage speakers and 30 L2 learners of Spanish completed four written tasks (acceptability judgment, truth-value judgment, picture-sentence matching, and sentence-picture acceptability judgment). The results show that the heritage speakers and the L2 learners exhibited dominant language transfer from English with the interpretation of definite articles in generic contexts; transfer effects were not as pronounced in the inalienable possession construction. We discuss the implications of these findings for heritage language research and teaching.