diff --git a/services/sensorservice/RotationVectorSensor.cpp b/services/sensorservice/RotationVectorSensor.cpp
index 6f4b8be..eecf260 100644
--- a/services/sensorservice/RotationVectorSensor.cpp
+++ b/services/sensorservice/RotationVectorSensor.cpp
@@ -114,10 +114,12 @@
         float qx = sqrtf( clamp( Hx - My - Az + 1) * 0.25f );
         float qy = sqrtf( clamp(-Hx + My - Az + 1) * 0.25f );
         float qz = sqrtf( clamp(-Hx - My + Az + 1) * 0.25f );
-        const float n = 1.0f / (qw*qw + qx*qx + qy*qy + qz*qz);
-        qx = copysignf(qx, Ay - Mz) * n;
-        qy = copysignf(qy, Hz - Ax) * n;
-        qz = copysignf(qz, Mx - Hy) * n;
+        qx = copysignf(qx, Ay - Mz);
+        qy = copysignf(qy, Hz - Ax);
+        qz = copysignf(qz, Mx - Hy);
+
+        // this quaternion is guaranteed to be normalized, by construction
+        // of the rotation matrix.
 
         *outEvent = event;
         outEvent->data[0] = qx;