diff --git a/ArduCopter/ArduCopter.pde b/ArduCopter/ArduCopter.pde
index 8369dcaa9c..c3fb1c7fbe 100644
--- a/ArduCopter/ArduCopter.pde
+++ b/ArduCopter/ArduCopter.pde
@@ -699,7 +699,7 @@ static int32_t home_bearing;
 static int32_t home_distance;
 // distance between plane and next_WP in cm
 // is not static because AP_Camera uses it
-int32_t wp_distance;
+uint32_t wp_distance;
 
 ////////////////////////////////////////////////////////////////////////////////
 // 3D Location vectors
diff --git a/ArduCopter/commands_logic.pde b/ArduCopter/commands_logic.pde
index 1f0a2097ca..ab9ef18822 100644
--- a/ArduCopter/commands_logic.pde
+++ b/ArduCopter/commands_logic.pde
@@ -391,14 +391,10 @@ static bool verify_nav_wp()
     }
 
     // Did we pass the WP?	// Distance checking
-    if((wp_distance <= (g.waypoint_radius * 100)) || check_missed_wp()) {
-        // if we have a distance calc error, wp_distance may be less than 0
-        if(wp_distance > 0) {
-            wp_verify_byte |= NAV_LOCATION;
-
-            if(loiter_time == 0) {
-                loiter_time = millis();
-            }
+    if((wp_distance <= (unsigned long)max((g.waypoint_radius * 100),0)) || check_missed_wp()) {
+        wp_verify_byte |= NAV_LOCATION;
+        if(loiter_time == 0) {
+            loiter_time = millis();
         }
     }
 
@@ -428,7 +424,7 @@ static bool verify_nav_wp()
 
 static bool verify_loiter_unlimited()
 {
-    if(nav_mode == NAV_WP &&  wp_distance <= (g.waypoint_radius * 100)) {
+    if(nav_mode == NAV_WP &&  wp_distance <= (unsigned long)max((g.waypoint_radius * 100),0)) {
         // switch to position hold
         set_nav_mode(NAV_LOITER);
     }
@@ -443,7 +439,7 @@ static bool verify_loiter_time()
             return true;
         }
     }
-    if(nav_mode == NAV_WP &&  wp_distance <= (g.waypoint_radius * 100)) {
+    if(nav_mode == NAV_WP &&  wp_distance <= (unsigned long)max((g.waypoint_radius * 100),0)) {
         // reset our loiter time
         loiter_time = millis();
         // switch to position hold
@@ -499,7 +495,7 @@ static bool verify_RTL()
 
         case RTL_STATE_RETURNING_HOME:
             // if we've reached home initiate loiter
-            if (wp_distance <= g.waypoint_radius * 100 || check_missed_wp()) {
+            if (wp_distance <= (unsigned long)max((g.waypoint_radius * 100),0) || check_missed_wp()) {
                 rtl_state = RTL_STATE_LOITERING_AT_HOME;
                 set_nav_mode(NAV_LOITER);
 
@@ -653,7 +649,7 @@ static bool verify_change_alt()
 static bool verify_within_distance()
 {
     //cliSerial->printf("cond dist :%d\n", (int)condition_value);
-    if (wp_distance < condition_value) {
+    if (wp_distance < max(condition_value,0)) {
         condition_value = 0;
         return true;
     }
diff --git a/ArduCopter/navigation.pde b/ArduCopter/navigation.pde
index 8d0f111ac5..2f5f1ab5db 100644
--- a/ArduCopter/navigation.pde
+++ b/ArduCopter/navigation.pde
@@ -565,7 +565,7 @@ static void update_crosstrack(void)
 {
     // Crosstrack Error
     // ----------------
-    if (wp_distance >= (g.crosstrack_min_distance * 100) &&
+    if (wp_distance >= (unsigned long)max((g.crosstrack_min_distance * 100),0) &&
         abs(wrap_180(wp_bearing - original_wp_bearing)) < 4500) {
 
 	    float temp = (wp_bearing - original_wp_bearing) * RADX100;
diff --git a/ArduPlane/ArduPlane.pde b/ArduPlane/ArduPlane.pde
index 7fce1772d7..64ee493b93 100644
--- a/ArduPlane/ArduPlane.pde
+++ b/ArduPlane/ArduPlane.pde
@@ -498,7 +498,7 @@ static int32_t nav_pitch_cd;
 ////////////////////////////////////////////////////////////////////////////////
 // Distance between plane and next waypoint.  Meters
 // is not static because AP_Camera uses it
-int32_t wp_distance;
+uint32_t wp_distance;
 
 // Distance between previous and next waypoint.  Meters
 static int32_t wp_totalDistance;
diff --git a/ArduPlane/commands_logic.pde b/ArduPlane/commands_logic.pde
index 3a7853ce16..b0dd836421 100644
--- a/ArduPlane/commands_logic.pde
+++ b/ArduPlane/commands_logic.pde
@@ -318,7 +318,7 @@ static bool verify_land()
 
     // Set land_complete if we are within 2 seconds distance or within
     // 3 meters altitude of the landing point
-    if (((wp_distance > 0) && (wp_distance <= (g.land_flare_sec*g_gps->ground_speed*0.01)))
+    if ((wp_distance <= (g.land_flare_sec*g_gps->ground_speed*0.01))
         || (adjusted_altitude_cm() <= next_WP.alt + g.land_flare_alt*100)) {
 
         land_complete = true;
@@ -359,7 +359,7 @@ static bool verify_nav_wp()
 {
     hold_course = -1;
     update_crosstrack();
-    if ((wp_distance > 0) && (wp_distance <= g.waypoint_radius)) {
+    if (wp_distance <= (unsigned)max(g.waypoint_radius,0)) {
         gcs_send_text_fmt(PSTR("Reached Waypoint #%i dist %um"),
                           (unsigned)nav_command_index,
                           (unsigned)get_distance(&current_loc, &next_WP));
@@ -416,7 +416,7 @@ static bool verify_loiter_turns()
 
 static bool verify_RTL()
 {
-    if (wp_distance <= g.waypoint_radius) {
+    if (wp_distance <= (unsigned)max(g.waypoint_radius,0)) {
         gcs_send_text_P(SEVERITY_LOW,PSTR("Reached home"));
         return true;
     }else{
@@ -477,7 +477,7 @@ static bool verify_change_alt()
 
 static bool verify_within_distance()
 {
-    if (wp_distance < condition_value) {
+    if (wp_distance < max(condition_value,0)) {
         condition_value = 0;
         return true;
     }
diff --git a/ArduPlane/navigation.pde b/ArduPlane/navigation.pde
index 4604bcfd45..20bba7a29b 100644
--- a/ArduPlane/navigation.pde
+++ b/ArduPlane/navigation.pde
@@ -148,11 +148,11 @@ static void update_loiter()
 {
     float power;
 
-    if(wp_distance <= g.loiter_radius) {
+    if(wp_distance <= (unsigned)max(g.loiter_radius,0)) {
         power = float(wp_distance) / float(g.loiter_radius);
         power = constrain(power, 0.5, 1);
         nav_bearing_cd += 9000.0 * (2.0 + power);
-    } else if(wp_distance < (g.loiter_radius + LOITER_RANGE)) {
+    } else if(wp_distance < (unsigned long)max((g.loiter_radius + LOITER_RANGE),0)) {
         power = -((float)(wp_distance - g.loiter_radius - LOITER_RANGE) / LOITER_RANGE);
         power = constrain(power, 0.5, 1);                               //power = constrain(power, 0, 1);
         nav_bearing_cd -= power * 9000;
@@ -191,7 +191,7 @@ static void update_crosstrack(void)
     // Crosstrack Error
     // ----------------
     // If we are too far off or too close we don't do track following
-    if (wp_totalDistance >= g.crosstrack_min_distance && 
+    if (wp_totalDistance >= (unsigned)max(g.crosstrack_min_distance,0) &&
         abs(wrap_180_cd(target_bearing_cd - crosstrack_bearing_cd)) < 4500) {
         // Meters we are off track line
         crosstrack_error = sinf(radians((target_bearing_cd - crosstrack_bearing_cd) * 0.01)) * wp_distance;               
diff --git a/libraries/AP_Math/AP_Math.h b/libraries/AP_Math/AP_Math.h
index 5f8b52d10e..1af688d130 100644
--- a/libraries/AP_Math/AP_Math.h
+++ b/libraries/AP_Math/AP_Math.h
@@ -51,7 +51,7 @@ enum Rotation           rotation_combination(enum Rotation r1, enum Rotation r2,
 float                   get_distance(const struct Location *loc1, const struct Location *loc2);
 
 // return distance in centimeters between two locations
-int32_t                 get_distance_cm(const struct Location *loc1, const struct Location *loc2);
+uint32_t                get_distance_cm(const struct Location *loc1, const struct Location *loc2);
 
 // return bearing in centi-degrees between two locations
 int32_t                 get_bearing_cd(const struct Location *loc1, const struct Location *loc2);
diff --git a/libraries/AP_Math/location.cpp b/libraries/AP_Math/location.cpp
index 97b13c4678..0089c1f0cd 100644
--- a/libraries/AP_Math/location.cpp
+++ b/libraries/AP_Math/location.cpp
@@ -43,22 +43,16 @@ static float longitude_scale(const struct Location *loc)
 
 
 
-// return distance in meters to between two locations, or -1
-// if one of the locations is invalid
+// return distance in meters to between two locations
 float get_distance(const struct Location *loc1, const struct Location *loc2)
 {
-    if (loc1->lat == 0 || loc1->lng == 0)
-        return -1;
-    if(loc2->lat == 0 || loc2->lng == 0)
-        return -1;
     float dlat              = (float)(loc2->lat - loc1->lat);
     float dlong             = ((float)(loc2->lng - loc1->lng)) * longitude_scale(loc2);
     return pythagorous2(dlat, dlong) * 0.01113195f;
 }
 
-// return distance in centimeters to between two locations, or -1 if
-// one of the locations is invalid
-int32_t get_distance_cm(const struct Location *loc1, const struct Location *loc2)
+// return distance in centimeters to between two locations
+uint32_t get_distance_cm(const struct Location *loc1, const struct Location *loc2)
 {
     return get_distance(loc1, loc2) * 100;
 }