Orthography is omnipresent in instructed L2 learning, and an increasing research pool investigates its effect on speech production and perception [1]. While orthography has facilitative effects on word learning and phonological accuracy [2], it may be detrimental on phonetic aspects of speech production and perception [3-4]. In classroom environments, students are frequently exposed to non-native speech through peers and teachers, which makes it difficult to ascribe non-native productions to orthographic influence alone. This study investigates if the presence and type of orthography affect phonetic properties of speech sound learning in production and perception. Seventy L1-Spanish speakers participated in a three-day vowel learning study. Participants were exposed to two unfamiliar vowels, /y/ and /ɛ/. Participants were assigned to three groups: The Conflicting Orthography group was exposed to the vowels in presence of the L1 graphemes <u> (corresponding to L1 /u/) and <e> (corresponding to L1 /e/), respectively. The Novel Orthography group was exposed to the same auditory stimuli in combination with grapheme-like symbols. The Auditory-only group was not exposed to any visual information. During exposure, participants listened to each vowel 1800 times and produced each vowel 600 times. On day 3, participants were tested on vowel production and perception. We hypothesized that conflicting orthography hinders successful learning of new speech sounds, while novel orthographic symbols improve learning outcomes. Moreover, given the acoustic similarity between /ɛ/ and L1 /e/, we expected learners in all groups to be more successful at learning /y/ than /ɛ/. The Conflicting Orthography group produced significantly lower F2 for /y/ than the Auditory-only group (*p*=0.0255), while the Novel Orthography group fell in between the other two groups. In perception, the Conflicting Orthography group categorized tokens with lower F2 as /y/ in comparison to the other two groups (*p*=0.002). The groups neither differed on their production nor perception of /ɛ/. Taken together, the results suggest that the presence of the grapheme <u> corresponding to L1-/u/, interfered with participants’ learning of /y/ in production and perception, while the presence of orthography did not influence learning outcomes for /ɛ/. These findings have important implications for current models of L2 speech production and perception. First, the results suggest that inconsistencies in grapheme-phoneme mappings in L1 and L2 can modulate phonetic aspects of speech production and perception in the earliest stages of L2 learning. Second, the results suggest that there is no one-fits-all effect of orthography on speech production and perception. While /y/ was affected by orthography in production and perception, no between-group differences were observed for /ɛ/. Moreover, only conflicting, but not novel orthography, influenced learning outcomes. These findings suggest that careful evaluation of sound contrasts and inconsistencies in L1-L2 grapheme-to-phoneme mappings are crucial in understanding L2 learning outcomes. References [1] Bassetti, B., Escudero, P., & Hayes-Harb, R. (2015). Second language phonology at the interface between acoustic and orthographic input. *Applied Psycholinguistics, 36*, 1–6. [2] Bürki, A., Welby, P., Clément, M., & Spinelli, E. (2019). Orthography and second language word learning: Moving beyond “friend or foe?”. *Journal of the Acoustical Society of America, 145*, EL265. [3] Escudero, P., Simon, E., & Mulak, K. E. (2014). Learning words in a new language: Orthography doesn't always help. Bilingualism: *Language and Cognition, 17*, 384–395. [4] Young-Scholten, M., & Langer, M. (2015). The role of orthographic input in second language German: Evidence from naturalistic adult learners’ production. *Applied Psycholinguistics, 36*, 93–114.