In this article, I examine how a focus on preciseness in the mathematics classroom could affect group activity. The preciseness relates to the ways mathematical concepts, in this case angles are described in discourse between students. In this context, I consider how 'micro-invalidations', can limit students' opportunities to learn in a social and language diverse classroom. I suggest that students and teachers do not merely navigate language diversity they also navigate epistemological aspects of mathematics. Learning to meet the knowledge of the Other, to avoid epistemological sanctions calls for meta understanding of language diversity which embrace epistemological aspects of mathematics.