diff --git a/src/xrt/auxiliary/math/m_api.h b/src/xrt/auxiliary/math/m_api.h
index fea003ecc..fdeebd22b 100644
--- a/src/xrt/auxiliary/math/m_api.h
+++ b/src/xrt/auxiliary/math/m_api.h
@@ -227,6 +227,19 @@ math_quat_finite_difference(const struct xrt_quat *quat0,
                             float dt,
                             struct xrt_vec3 *out_ang_vel);
 
+
+/*
+ *
+ * Matrix function
+ *
+ */
+
+void
+math_matrix_3x3_transform_vec3(const struct xrt_matrix_3x3 *left,
+                               const struct xrt_vec3 *right,
+                               struct xrt_vec3 *result);
+
+
 /*
  *
  * Pose functions.
diff --git a/src/xrt/auxiliary/math/m_base.cpp b/src/xrt/auxiliary/math/m_base.cpp
index 0d8878450..ad39b4d81 100644
--- a/src/xrt/auxiliary/math/m_base.cpp
+++ b/src/xrt/auxiliary/math/m_base.cpp
@@ -196,6 +196,26 @@ math_quat_rotate_vec3(const struct xrt_quat *left,
 }
 
 
+/*
+ *
+ * Exported pose functions.
+ *
+ */
+
+extern "C" void
+math_matrix_3x3_transform_vec3(const struct xrt_matrix_3x3 *left,
+                               const struct xrt_vec3 *right,
+                               struct xrt_vec3 *result)
+{
+	Eigen::Matrix3f m;
+	m << left->v[0], left->v[1], left->v[2], // 1
+	    left->v[3], left->v[4], left->v[5],  // 2
+	    left->v[6], left->v[7], left->v[8];  // 3
+
+	map_vec3(*result) = m * copy(right);
+}
+
+
 /*
  *
  * Exported pose functions.