diff --git a/libraries/AP_GPS/AP_GPS.cpp b/libraries/AP_GPS/AP_GPS.cpp
index c6e30bd5a4..570cfae930 100644
--- a/libraries/AP_GPS/AP_GPS.cpp
+++ b/libraries/AP_GPS/AP_GPS.cpp
@@ -256,24 +256,28 @@ AP_GPS::update(void)
   set HIL (hardware in the loop) status for a GPS instance
  */
 void 
-AP_GPS::setHIL(GPS_Status _status, uint64_t time_epoch_ms, 
-               Location &_location, Vector3f &_velocity, uint8_t _num_sats)
+AP_GPS::setHIL(uint8_t instance, GPS_Status _status, uint64_t time_epoch_ms, 
+               Location &_location, Vector3f &_velocity, uint8_t _num_sats, 
+               uint16_t hdop, bool _have_vertical_velocity)
 {
+    if (instance >= GPS_MAX_INSTANCES) {
+        return;
+    }
     uint32_t tnow = hal.scheduler->millis();
-    GPS_State &istate = state[0];
+    GPS_State &istate = state[instance];
     istate.status = _status;
     istate.location = _location;
     istate.location.options = 0;
     istate.velocity = _velocity;
     istate.ground_speed = pythagorous2(istate.velocity.x, istate.velocity.y);
     istate.ground_course_cd = degrees(atan2f(istate.velocity.y, istate.velocity.x)) * 100UL;
-    istate.hdop = 0;
+    istate.hdop = hdop;
     istate.num_sats = _num_sats;
-    istate.have_vertical_velocity = false;
+    istate.have_vertical_velocity = _have_vertical_velocity;
     istate.last_gps_time_ms = tnow;
     istate.time_week     = time_epoch_ms / (86400*7*(uint64_t)1000);
     istate.time_week_ms  = time_epoch_ms - istate.time_week*(86400*7*(uint64_t)1000);
-    timing[0].last_message_time_ms = tnow;
-    timing[0].last_fix_time_ms = tnow;
-    _type[0].set(GPS_TYPE_HIL);
+    timing[instance].last_message_time_ms = tnow;
+    timing[instance].last_fix_time_ms = tnow;
+    _type[instance].set(GPS_TYPE_HIL);
 }
diff --git a/libraries/AP_GPS/AP_GPS.h b/libraries/AP_GPS/AP_GPS.h
index beab3cd53e..3c7c1bc936 100644
--- a/libraries/AP_GPS/AP_GPS.h
+++ b/libraries/AP_GPS/AP_GPS.h
@@ -104,7 +104,7 @@ public:
         Location location;                  ///< last fix location
         float ground_speed;                 ///< ground speed in m/sec
         int32_t ground_course_cd;           ///< ground course in 100ths of a degree
-        int16_t hdop;                       ///< horizontal dilution of precision in cm
+        uint16_t hdop;                      ///< horizontal dilution of precision in cm
         uint8_t num_sats;                   ///< Number of visible satelites        
         Vector3f velocity;                  ///< 3D velocitiy in m/s, in NED format
         bool have_vertical_velocity:1;      ///< does this GPS give vertical velocity?
@@ -192,10 +192,10 @@ public:
     }
 
     // horizontal dilution of precision
-    int16_t get_hdop(uint8_t instance) const {
+    uint16_t get_hdop(uint8_t instance) const {
         return state[instance].hdop;
     }
-    int16_t get_hdop() const {
+    uint16_t get_hdop() const {
         return get_hdop(primary_instance());
     }
 
@@ -235,8 +235,9 @@ public:
     float get_lag() const { return 0.2f; }
 
     // set position for HIL
-    void setHIL(GPS_Status status, uint64_t time_epoch_ms, 
-                Location &location, Vector3f &velocity, uint8_t num_sats);
+    void setHIL(uint8_t instance, GPS_Status status, uint64_t time_epoch_ms, 
+                Location &location, Vector3f &velocity, uint8_t num_sats,
+                uint16_t hdop, bool _have_vertical_velocity);
 
     static const struct AP_Param::GroupInfo var_info[];
 
diff --git a/libraries/AP_GPS/AP_GPS_NMEA.h b/libraries/AP_GPS/AP_GPS_NMEA.h
index f429bde6ae..f85c86b318 100644
--- a/libraries/AP_GPS/AP_GPS_NMEA.h
+++ b/libraries/AP_GPS/AP_GPS_NMEA.h
@@ -133,7 +133,7 @@ private:
     int32_t _new_altitude;                                      ///< altitude parsed from a term
     int32_t _new_speed;                                                 ///< speed parsed from a term
     int32_t _new_course;                                        ///< course parsed from a term
-    int16_t _new_hdop;                                                  ///< HDOP parsed from a term
+    uint16_t _new_hdop;                                                 ///< HDOP parsed from a term
     uint8_t _new_satellite_count;                       ///< satellite count parsed from a term
 
     /// @name	Init strings