This case study examines how a lecturer and a group of students adjust to a request for English-only medium of instruction in tertiary education. The study draws on sociocultural theories considering context and language use as tools for meaning making. Goffman's theories of stage setting and footing are used to analyse how the lecturer positions himself in relation to language use. The findings show that in the observed session the lecturer used code-switching as a tool to extend students' academic literacy. Further, we found that he in most cases assigned different classroom spaces to different languages. Hence, English as the targeted language of instruction was used when the lecturer was standing at the board, the official teaching space, whereas French, a previously accepted language, was used in a semi-official space closer to the students. Kinyarwanda, the lecturer's and students' first language, is not permitted as a medium of instruction, but was used when the lecturer was close to the students. We label this a personal space, where the lecturer changed code in order to improve interaction and students' understanding. Such code-switching has cultural and historical traditions and is viewed in this study as a strategy to avoid misunderstandings and allow more equitable learning opportunities. (Contains 1 table and 2 figures.)