diff --git a/libraries/AP_GPS/AP_GPS.cpp b/libraries/AP_GPS/AP_GPS.cpp
index ef30533416..b62f98209c 100644
--- a/libraries/AP_GPS/AP_GPS.cpp
+++ b/libraries/AP_GPS/AP_GPS.cpp
@@ -772,6 +772,8 @@ void AP_GPS::update_instance(uint8_t instance)
  */
 void AP_GPS::update(void)
 {
+    WITH_SEMAPHORE(rsem);
+
     for (uint8_t i=0; i<GPS_MAX_RECEIVERS; i++) {
         update_instance(i);
     }
diff --git a/libraries/AP_GPS/AP_GPS.h b/libraries/AP_GPS/AP_GPS.h
index e37bdcc81d..5b119dd83e 100644
--- a/libraries/AP_GPS/AP_GPS.h
+++ b/libraries/AP_GPS/AP_GPS.h
@@ -74,6 +74,11 @@ public:
         return _singleton;
     }
 
+    // allow threads to lock against GPS update
+    HAL_Semaphore &get_semaphore(void) {
+        return rsem;
+    }
+    
     // GPS driver types
     enum GPS_Type {
         GPS_TYPE_NONE  = 0,
@@ -488,6 +493,7 @@ protected:
 
 private:
     static AP_GPS *_singleton;
+    HAL_Semaphore_Recursive rsem;
 
     // returns the desired gps update rate in milliseconds
     // this does not provide any guarantee that the GPS is updating at the requested