diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h b/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h
index 27694752e9..5ae14f0d5b 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h
@@ -74,7 +74,7 @@ public:
 
     // 0 is no return value, 100 is perfect.  false means signal
     // quality is not available
-    virtual bool get_signal_quality_pct(uint8_t &quality_pct) const { return false; }
+    virtual bool get_signal_quality_pct(int8_t &quality_pct) const { return false; }
 
     // return the actual type of the rangefinder, as opposed to the
     // parameter value which may be changed at runtime.
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareSerial.h b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareSerial.h
index 17b5ef46ea..cbdfe5d6a5 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareSerial.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareSerial.h
@@ -26,7 +26,7 @@ protected:
         return MAV_DISTANCE_SENSOR_LASER;
     }
 
-    bool get_signal_quality_pct(uint8_t &quality_pct) const override {
+    bool get_signal_quality_pct(int8_t &quality_pct) const override {
         quality_pct = no_signal ? 0 : 100;
         return true;
     }