diff --git a/ArduPlane/Attitude.pde b/ArduPlane/Attitude.pde
index 8f7429c462..51f83fba24 100644
--- a/ArduPlane/Attitude.pde
+++ b/ArduPlane/Attitude.pde
@@ -358,7 +358,7 @@ static void set_servos(void)
 			*/
 			if (
 					(control_mode == CIRCLE || control_mode >= FLY_BY_WIRE_B) &&
-					(abs(home.alt - current_loc.alt) < 1000) &&
+					(labs(home.alt - current_loc.alt) < 1000) &&
 					((airspeed.use()? airspeed.get_airspeed_cm() : g_gps->ground_speed) < 500 ) &&
 					!(control_mode==AUTO && takeoff_complete == false)
 				) {
diff --git a/ArduPlane/commands_logic.pde b/ArduPlane/commands_logic.pde
index c2550f2213..c84e189330 100644
--- a/ArduPlane/commands_logic.pde
+++ b/ArduPlane/commands_logic.pde
@@ -435,7 +435,7 @@ static void do_wait_delay()
 
 static void do_change_alt()
 {
-	condition_rate		= abs((int)next_nonnav_command.lat);
+	condition_rate		= labs((int)next_nonnav_command.lat);
 	condition_value 	= next_nonnav_command.alt;
 	if(condition_value < current_loc.alt) condition_rate = -condition_rate;
 	target_altitude_cm	= current_loc.alt + (condition_rate / 10);		// Divide by ten for 10Hz update
diff --git a/libraries/AP_Math/examples/location/location.pde b/libraries/AP_Math/examples/location/location.pde
index 9b569a8aeb..aaea96b53c 100644
--- a/libraries/AP_Math/examples/location/location.pde
+++ b/libraries/AP_Math/examples/location/location.pde
@@ -104,7 +104,7 @@ static void test_one_offset(struct Location &loc,
         brg_error += 360;
     }
 
-    if (abs(dist - dist2) > 1.0 ||
+    if (fabs(dist - dist2) > 1.0 ||
         brg_error > 1.0) {
         Serial.printf("Failed offset test brg_error=%f dist_error=%f\n",
                       brg_error, dist-dist2);
diff --git a/libraries/AP_Navigation/Navigation.cpp b/libraries/AP_Navigation/Navigation.cpp
index 9802257a89..c38e1c8b38 100644
--- a/libraries/AP_Navigation/Navigation.cpp
+++ b/libraries/AP_Navigation/Navigation.cpp
@@ -117,7 +117,7 @@ void
 Navigation::calc_long_scaling(int32_t lat)
 {
 	// this is used to offset the shrinking longitude as we go towards the poles	
-	float rads 			= (abs(lat) / T7) * 0.0174532925;
+	float rads 			= (fabs(lat) / T7) * 0.0174532925;
 	_scaleLongDown 		= cos(rads);
 	_scaleLongUp 		= 1.0f / cos(rads);
 }