This study analysed the extent to which literate native speakers of a language with a phonemic alphabetic orthography rely on their first language (L1) orthography during second language (L2) speech production of a language that has a morphophonemic alphabetic orthography. The production of the English flapping rule by 15 adult native speakers of Spanish (NSS) was analysed. Flap production should not be problematic for NSS learning English as L2, since the flap [r] exists in the Spanish phonemic inventory and it has similar acoustic, articluatory, and distributional properties in English and Spanish. However, this study hypothesizes that access to the flap is blocked by NSS participants' lack of phonological awareness in English, which is brought about by the participants' reliance on the Spanish orthographic system, since the graphs used to represent the English flap intervocalically have either different surface realizations in Spanish (such as [t] and [d]) or have no equivalents in the Spanish orthographic system (such as [tt] and [dd]). It was found that NSS relied on the Spanish orthographic system at a statistically significant level, despite both languages having alphabetic orthographies and sharing the same visual code. Less reliance on L1 orthography was observed in frequent L2 lexical items, demonstrating that negative effects of L1 orthography are inversely correlated to familiarity with L2 lexical items and that frequent lexical items promote L2 phonological awareness. (Contains 1 note, 4 tables, and 4 figures.)