diff --git a/libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp b/libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp
index 051f439017..b03b103431 100644
--- a/libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp
+++ b/libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp
@@ -125,7 +125,7 @@ float AP_InertialNav_NavEKF::get_altitude() const
  *
  * @return
  */
-bool AP_InertialNav_NavEKF::get_hagl(float height) const
+bool AP_InertialNav_NavEKF::get_hagl(float &height) const
 {
     // true when estimate is valid
     bool valid = _ahrs_ekf.get_NavEKF().getHAGL(height);
diff --git a/libraries/AP_InertialNav/AP_InertialNav_NavEKF.h b/libraries/AP_InertialNav/AP_InertialNav_NavEKF.h
index c5c5af18a3..e64e342270 100644
--- a/libraries/AP_InertialNav/AP_InertialNav_NavEKF.h
+++ b/libraries/AP_InertialNav/AP_InertialNav_NavEKF.h
@@ -92,7 +92,7 @@ public:
      * getHgtAboveGnd - get latest altitude estimate above ground level in centimetres and validity flag
      * @return
      */
-    bool       get_hagl(float hagl) const;
+    bool       get_hagl(float &hagl) const;
 
     /**
      * get_hgt_ctrl_limit - get maximum height to be observed by the control loops in cm and a validity flag