diff --git a/src/xrt/auxiliary/math/m_api.h b/src/xrt/auxiliary/math/m_api.h
index f01607934..829f0a116 100644
--- a/src/xrt/auxiliary/math/m_api.h
+++ b/src/xrt/auxiliary/math/m_api.h
@@ -413,6 +413,15 @@ math_quat_from_swing(const struct xrt_vec2 *swing, struct xrt_quat *result);
 void
 math_quat_from_swing_twist(const struct xrt_vec2 *swing, const float twist, struct xrt_quat *result);
 
+/*!
+ * Converts a quaternion to XY-swing and Z-twist
+ *
+ * @relates xrt_quat
+ * @ingroup aux_math
+ */
+void
+math_quat_to_swing_twist(const struct xrt_quat *in, struct xrt_vec2 *out_swing, float *out_twist);
+
 /*
  *
  * Matrix functions
diff --git a/src/xrt/auxiliary/math/m_base.cpp b/src/xrt/auxiliary/math/m_base.cpp
index 7c72dc026..4677f0598 100644
--- a/src/xrt/auxiliary/math/m_base.cpp
+++ b/src/xrt/auxiliary/math/m_base.cpp
@@ -484,6 +484,34 @@ math_quat_from_swing_twist(const struct xrt_vec2 *swing, const float twist, stru
 	}
 }
 
+/*!
+ * Converts a quaternion to XY-swing and Z-twist
+ *
+ * @relates xrt_quat
+ * @ingroup aux_math
+ */
+extern "C" void
+math_quat_to_swing_twist(const struct xrt_quat *in, struct xrt_vec2 *out_swing, float *out_twist)
+{
+	Eigen::Quaternionf rot = map_quat(*in);
+
+	Eigen::Vector3f our_z = rot * (Eigen::Vector3f::UnitZ());
+
+	Eigen::Quaternionf swing = Eigen::Quaternionf().setFromTwoVectors(Eigen::Vector3f::UnitZ(), our_z);
+
+	Eigen::Quaternionf twist = swing.inverse() * rot;
+
+	Eigen::AngleAxisf twist_aax = Eigen::AngleAxisf(twist);
+
+	Eigen::AngleAxisf swing_aax = Eigen::AngleAxisf(swing);
+
+	out_swing->x = swing_aax.axis().x() * swing_aax.angle();
+	out_swing->y = swing_aax.axis().y() * swing_aax.angle();
+	assert(swing_aax.axis().z() < 0.001);
+
+	*out_twist = twist_aax.axis().z() * twist_aax.angle();
+}
+
 /*
  *
  * Exported matrix functions.