diff --git a/libraries/AP_GPS/GPS.h b/libraries/AP_GPS/GPS.h
index d935a260ab..faee865213 100644
--- a/libraries/AP_GPS/GPS.h
+++ b/libraries/AP_GPS/GPS.h
@@ -25,7 +25,7 @@ public:
     ///
     void			update(void);
 
-    void (*callback)(uint32_t t);
+    void (*callback)(unsigned long t);
 
     /// GPS status codes
     ///