diff --git a/libraries/AP_GPS/GPS.cpp b/libraries/AP_GPS/GPS.cpp
index 6fcde0429a..e917cf4458 100644
--- a/libraries/AP_GPS/GPS.cpp
+++ b/libraries/AP_GPS/GPS.cpp
@@ -36,9 +36,9 @@ GPS::update(void)
 
 		if (_status == GPS_OK) {
 			// update our acceleration
-			float deltat = 1.0e-3 * (_idleTimer - _last_fix_time);
+			float deltat = 1.0e-3 * (_idleTimer - last_fix_time);
 			float deltav = 1.0e-2 * ((float)ground_speed - (float)_last_ground_speed);
-			_last_fix_time = _idleTimer;
+			last_fix_time = _idleTimer;
 			_last_ground_speed = ground_speed;
 
 			if (deltat > 2.0 || deltat == 0) {
diff --git a/libraries/AP_GPS/GPS.h b/libraries/AP_GPS/GPS.h
index 9889f96a02..1638d76a8c 100644
--- a/libraries/AP_GPS/GPS.h
+++ b/libraries/AP_GPS/GPS.h
@@ -113,6 +113,9 @@ public:
 	// our approximate linear acceleration in m/s/s
 	float acceleration(void) { return _acceleration; }
 
+	// the time we got our last fix in system milliseconds
+	uint32_t last_fix_time;
+
 protected:
     Stream	*_port;			///< port the GPS is attached to
 
@@ -173,9 +176,6 @@ private:
     /// Our current status
     GPS_Status					_status;
 
-	// the time we got our last fix in system milliseconds
-	uint32_t _last_fix_time;
-
 	// previous ground speed in cm/s
     uint32_t _last_ground_speed;