diff --git a/src/xrt/auxiliary/math/m_vec2.h b/src/xrt/auxiliary/math/m_vec2.h
index fe8cf3dad..76b6337fb 100644
--- a/src/xrt/auxiliary/math/m_vec2.h
+++ b/src/xrt/auxiliary/math/m_vec2.h
@@ -96,6 +96,12 @@ m_vec2_normalize(struct xrt_vec2 *inout)
 	*inout = m_vec2_div_scalar(*inout, m_vec2_len(*inout));
 }
 
+static inline float
+m_vec2_cross(struct xrt_vec2 l, struct xrt_vec2 r)
+{
+	return l.x * r.y - r.x * l.y;
+}
+
 static inline float
 m_vec2_dot(struct xrt_vec2 l, struct xrt_vec2 r)
 {