Acquiring a second alphabetic language also entails learning a new set of orthographic rules and specific patterns of grapheme combinations (namely, the orthotactics). The present longitudinal study aims to investigate whether orthotactic sensitivity changes over the course of a second language learning program. To this end, a group of Spanish monolingual old adults completed a Basque language learning course. They were tested in different moments with a language decision task that included pseudowords that could be Basque-marked, Spanish-marked or neutral. Results showed that the markedness effect varied as a function of second language acquisition, showing that learning a second language changes the sensitivity not only to the orthographic patterns of the newly acquired language, but to those of the native language too. These results demonstrate that the orthographic representations of the native language are not static and that experience with a second language boosts markedness perception in the first language.