diff --git a/libraries/AP_OpticalFlow/OpticalFlow.h b/libraries/AP_OpticalFlow/OpticalFlow.h
index a056a4e771..4caf99482e 100644
--- a/libraries/AP_OpticalFlow/OpticalFlow.h
+++ b/libraries/AP_OpticalFlow/OpticalFlow.h
@@ -74,7 +74,7 @@ public:
     void setHIL(const struct OpticalFlow_state &state);
 
     // return a 3D vector defining the position offset of the sensors focal point in metres relative to the body frame origin
-    const Vector3f get_pos_offset(void) const {
+    const Vector3f &get_pos_offset(void) const {
         return _pos_offset;
     }