This article presents a case study that examines the level of integration of mathematical knowledge in physics problem solving among first grade students of upper secondary school. We explore the ways in which two specific students utilize their knowledge and we attempt to identify the epistemological framings they refer to while solving a physics problem. Participant observation was used for data collection, and the students' verbal interactions were video-recorded. The analysis shows that they tend to use a wide spectrum of epistemological framings that entangle mathematics and physics but at the same time face significant practical difficulties in modulating the two subjects.