The present study explores how classroom participants invoke a monolingual target-language policy in an English as a foreign language (EFL) classroom, specifically focusing on one method of doing language policy through self-initiated language policing sequences, which I have called "self-policing." Language policing refers to the mechanism deployed by the teacher and/or the pupils to (re-)establish the normatively prescribed medium of classroom interaction (Amir & Musk, 2013; cf. Bonacina & Gafaranga, 2011). The data comes from sequential analyses of 20 hours of video recordings in grades 8 & 9 of an international compulsory school in Sweden between the years 2007-2010. Drawing on Auer (1984) and Gafaranga's (1999) organisational code-switching framework, this study sheds light on how teachers and pupils self-initiate a switch to English in their interactions. As will be demonstrated, both teachers and pupils, while orienting to the English-only norm, use a three-step sequence for language policing.