ABSTRACT Despite growing literature on EMI policy implementation in higher education contexts, there is a lack of research on how these policies are enacted at the micro-level, particularly in the classroom settings. The present study explores the language beliefs and practices of a psychology professor in two English-medium instruction (EMI) courses which differed in course types and students’ preparedness, in an effort to understand how language policy was enacted in nuanced EMI settings. Drawing on semi-structured interviews, classroom observation, and course artifacts, the study reveals that the non-native English speaking participant held a consistent belief in enforcing a strict English-only policy within the classroom, yet she managed students’ and her own language practices slightly differently (e.g. speak time, pace, vocabulary, L1 proportion) based on specific course objectives. The findings highlight the importance of consistent and mindful language policies that allow for flexible implementation where unique features of individual EMI contexts are accommodated. Through highlighting the agency of EMI teachers as language policy arbiters, we reimagined the original ROAD-MAPPING framework [Dafouz, E., & Smit, U. (2016). Toward a dynamic conceptual framework for English-medium education in multilingual university settings. Applied Linguistics, 37(3), 397–415] to capture the granular and dynamic process of EMI policy enactment and implementation in authentic classrooms. Practical implications are drawn accordingly.