diff --git a/APMrover2/sensors.cpp b/APMrover2/sensors.cpp
index cddead068c..cb90bee5be 100644
--- a/APMrover2/sensors.cpp
+++ b/APMrover2/sensors.cpp
@@ -67,8 +67,8 @@ void Rover::read_sonars(void)
         // we have two sonars
         obstacle.sonar1_distance_cm = sonar.distance_cm(0);
         obstacle.sonar2_distance_cm = sonar.distance_cm(1);
-        if (obstacle.sonar1_distance_cm <= (uint16_t)g.sonar_trigger_cm &&
-            obstacle.sonar1_distance_cm <= (uint16_t)obstacle.sonar2_distance_cm)  {
+        if (obstacle.sonar1_distance_cm < (uint16_t)g.sonar_trigger_cm &&
+            obstacle.sonar1_distance_cm < (uint16_t)obstacle.sonar2_distance_cm)  {
             // we have an object on the left
             if (obstacle.detected_count < 127) {
                 obstacle.detected_count++;
@@ -79,7 +79,7 @@ void Rover::read_sonars(void)
             }
             obstacle.detected_time_ms = AP_HAL::millis();
             obstacle.turn_angle = g.sonar_turn_angle;
-        } else if (obstacle.sonar2_distance_cm <= (uint16_t)g.sonar_trigger_cm) {
+        } else if (obstacle.sonar2_distance_cm < (uint16_t)g.sonar_trigger_cm) {
             // we have an object on the right
             if (obstacle.detected_count < 127) {
                 obstacle.detected_count++;
@@ -95,7 +95,7 @@ void Rover::read_sonars(void)
         // we have a single sonar
         obstacle.sonar1_distance_cm = sonar.distance_cm(0);
         obstacle.sonar2_distance_cm = 0;
-        if (obstacle.sonar1_distance_cm <= (uint16_t)g.sonar_trigger_cm)  {
+        if (obstacle.sonar1_distance_cm < (uint16_t)g.sonar_trigger_cm)  {
             // obstacle detected in front 
             if (obstacle.detected_count < 127) {
                 obstacle.detected_count++;