diff --git a/EKF/ekf.h b/EKF/ekf.h
index 4e2964e700..b77aa681f8 100644
--- a/EKF/ekf.h
+++ b/EKF/ekf.h
@@ -795,7 +795,7 @@ private:
 
 	// calculate a synthetic value for the magnetometer Z component, given the 3D magnetomter
 	// sensor measurement
-	float calculate_synthetic_mag_z_measurement(Vector3f mag_meas, Vector3f mag_earth_predicted);
+	float calculate_synthetic_mag_z_measurement(const Vector3f& mag_meas, const Vector3f& mag_earth_predicted);
 
 	void stopGpsFusion();
 
diff --git a/EKF/mag_fusion.cpp b/EKF/mag_fusion.cpp
index c6041793c4..744825acf6 100644
--- a/EKF/mag_fusion.cpp
+++ b/EKF/mag_fusion.cpp
@@ -997,7 +997,7 @@ void Ekf::limitDeclination()
 	}
 }
 
-float Ekf::calculate_synthetic_mag_z_measurement(Vector3f mag_meas, Vector3f mag_earth_predicted)
+float Ekf::calculate_synthetic_mag_z_measurement(const Vector3f& mag_meas, const Vector3f& mag_earth_predicted)
 {
 	// theoretical magnitude of the magnetometer Z component value given X and Y sensor measurement and our knowledge
 	// of the earth magnetic field vector at the current location