diff --git a/ArduPlane/ArduPlane.pde b/ArduPlane/ArduPlane.pde
index 9d52939a30..ae771368ad 100644
--- a/ArduPlane/ArduPlane.pde
+++ b/ArduPlane/ArduPlane.pde
@@ -285,7 +285,9 @@ static AP_YawController   yawController(ahrs, aparm);
 static AP_SteerController steerController(ahrs);
 
 // Inertial Navigation EKF
+#if HAL_CPU_CLASS >= HAL_CPU_CLASS_150
 static NavEKF NavEKF(ahrs, barometer);
+#endif
 
 #if CONFIG_HAL_BOARD == HAL_BOARD_AVR_SITL
 SITL sitl;
@@ -805,7 +807,9 @@ static void ahrs_update()
 #endif
 
     ahrs.update();
+#if HAL_CPU_CLASS >= HAL_CPU_CLASS_150
     NavEKF.UpdateFilter();
+#endif
 
     if (should_log(MASK_LOG_ATTITUDE_FAST)) {
         Log_Write_Attitude();
diff --git a/ArduPlane/GCS_Mavlink.pde b/ArduPlane/GCS_Mavlink.pde
index e61a197425..e805617e4b 100644
--- a/ArduPlane/GCS_Mavlink.pde
+++ b/ArduPlane/GCS_Mavlink.pde
@@ -530,6 +530,7 @@ static void NOINLINE send_simstate(mavlink_channel_t chan)
 // report NavEKF state
 static void NOINLINE send_ekf(mavlink_channel_t chan)
 {
+#if HAL_CPU_CLASS >= HAL_CPU_CLASS_150
     Vector3f euler;
     struct Location loc;
     NavEKF.getEulerAngles(euler);
@@ -541,6 +542,7 @@ static void NOINLINE send_ekf(mavlink_channel_t chan)
                          loc.alt*1.0e-2f,
                          loc.lat,
                          loc.lng);
+#endif
 }
 
 static void NOINLINE send_hwstatus(mavlink_channel_t chan)
diff --git a/ArduPlane/Log.pde b/ArduPlane/Log.pde
index b5bbfac70f..762af324aa 100644
--- a/ArduPlane/Log.pde
+++ b/ArduPlane/Log.pde
@@ -203,6 +203,7 @@ struct PACKED log_EKF {
 // Write an EKF packet
 static void Log_Write_EKF(void)
 {
+#if HAL_CPU_CLASS >= HAL_CPU_CLASS_150
     Vector3f euler;
     struct Location loc;
     NavEKF.getEulerAngles(euler);
@@ -218,6 +219,7 @@ static void Log_Write_EKF(void)
         lon     : loc.lng
     };
     DataFlash.WriteBlock(&pkt, sizeof(pkt));
+#endif
 }
 
 struct PACKED log_Performance {
diff --git a/ArduPlane/commands.pde b/ArduPlane/commands.pde
index 0f535012c7..42d3494bed 100644
--- a/ArduPlane/commands.pde
+++ b/ArduPlane/commands.pde
@@ -241,7 +241,9 @@ static void init_home()
     guided_WP.alt += g.RTL_altitude_cm;
 
     // startup EKF now we have home
+#if HAL_CPU_CLASS >= HAL_CPU_CLASS_150
     NavEKF.InitialiseFilter();
+#endif
 }
 
 /*