diff --git a/libraries/AP_GPS/AP_GPS.cpp b/libraries/AP_GPS/AP_GPS.cpp
index 1566e072d9..6116ca2500 100644
--- a/libraries/AP_GPS/AP_GPS.cpp
+++ b/libraries/AP_GPS/AP_GPS.cpp
@@ -611,7 +611,7 @@ AP_GPS::setHIL(uint8_t instance, GPS_Status _status, uint64_t time_epoch_ms,
     istate.hdop = hdop;
     istate.num_sats = _num_sats;
     istate.last_gps_time_ms = tnow;
-    uint64_t gps_time_ms = time_epoch_ms - UNIX_OFFSET;
+    uint64_t gps_time_ms = time_epoch_ms - UNIX_OFFSET_MSEC;
     istate.time_week     = gps_time_ms / MSEC_PER_WEEK;
     istate.time_week_ms  = gps_time_ms - istate.time_week * MSEC_PER_WEEK;
     timing[instance].last_message_time_ms = tnow;
diff --git a/libraries/AP_GPS/AP_GPS.h b/libraries/AP_GPS/AP_GPS.h
index c97d4c7c6c..1521761f84 100644
--- a/libraries/AP_GPS/AP_GPS.h
+++ b/libraries/AP_GPS/AP_GPS.h
@@ -34,7 +34,7 @@
 // the number of GPS leap seconds
 #define GPS_LEAPSECONDS_MILLIS 18000ULL
 
-#define UNIX_OFFSET (17000ULL * 86400ULL + 52 * 10 * MSEC_PER_WEEK - GPS_LEAPSECONDS_MILLIS)
+#define UNIX_OFFSET_MSEC (17000ULL * 86400ULL + 52 * 10 * MSEC_PER_WEEK - GPS_LEAPSECONDS_MILLIS)
 
 class DataFlash_Class;
 class AP_GPS_Backend;
diff --git a/libraries/AP_GPS/GPS_Backend.cpp b/libraries/AP_GPS/GPS_Backend.cpp
index 997a2902b8..3b9e1b3304 100644
--- a/libraries/AP_GPS/GPS_Backend.cpp
+++ b/libraries/AP_GPS/GPS_Backend.cpp
@@ -63,7 +63,7 @@ int16_t AP_GPS_Backend::swap_int16(int16_t v) const
  */
 uint64_t AP_GPS::time_epoch_convert(uint16_t gps_week, uint32_t gps_ms)
 {
-    uint64_t fix_time_ms = UNIX_OFFSET + gps_week * MSEC_PER_WEEK + gps_ms;
+    uint64_t fix_time_ms = UNIX_OFFSET_MSEC + gps_week * MSEC_PER_WEEK + gps_ms;
     return fix_time_ms;
 }