Related languages, like English and Spanish, often have similar orthographies but use the same letters for different sounds. Learning a second language frequently involves learning additional letter-sound mappings that mismatch native language mappings. In the current study, we investigated whether L2 spoken words activate L2 orthography despite conflict with L1 orthography-to-phonology mappings. Participants first learned an artificial language with letter-sound mappings that mismatched English (e.g., the letter 'G' represented /h/, and the word /gufo/ was spelled 'hane'). Next, fixations of L1 orthographic competitors (e.g., 'cane') in response to auditory L2 input (e.g., /gufo/) were assessed using the visual world paradigm. Results showed that participants fixated L1 competitors that overlapped with targets orthographically (but not phonologically) more than unrelated fillers. We conclude that second language learners can rapidly acquire novel letter-sound mappings, and words based on these mappings are integrated into the existing lexicon, activating orthographic competitors in the native language.