diff --git a/libraries/AP_Airspeed/Airspeed_Calibration.cpp b/libraries/AP_Airspeed/Airspeed_Calibration.cpp
index 1d576323ec..c73fee8238 100644
--- a/libraries/AP_Airspeed/Airspeed_Calibration.cpp
+++ b/libraries/AP_Airspeed/Airspeed_Calibration.cpp
@@ -54,7 +54,7 @@ float Airspeed_Calibration::update(float airspeed, const Vector3f &vg)
     // No state prediction required because states are assumed to be time
     // invariant plus process noise
     // Ignore vertical wind component
-    float TAS_pred = state.z * sqrtf(sq(vg.x - state.x) + sq(vg.y - state.y) + sq(vg.z));
+    float TAS_pred = state.z * pythagorous3(vg.x - state.x, vg.y - state.y, vg.z);
     float TAS_mea  = airspeed;
     
     // Calculate the observation Jacobian H_TAS