diff --git a/libraries/AP_GPS/AP_GPS.cpp b/libraries/AP_GPS/AP_GPS.cpp
index f36cbe9dd6..72f9dc5c68 100644
--- a/libraries/AP_GPS/AP_GPS.cpp
+++ b/libraries/AP_GPS/AP_GPS.cpp
@@ -519,7 +519,7 @@ uint64_t AP_GPS::time_epoch_usec(uint8_t instance) const
     uint64_t fix_time_ms;
     // add in the time since the last fix message
     if (istate.last_corrected_gps_time_us != 0) {
-        fix_time_ms = time_epoch_convert(istate.time_week, drivers[instance]->get_last_itow());
+        fix_time_ms = time_epoch_convert(istate.time_week, drivers[instance]->get_last_itow_ms());
         return (fix_time_ms*1000ULL) + (AP_HAL::micros64() - istate.last_corrected_gps_time_us);
     } else {
         fix_time_ms = time_epoch_convert(istate.time_week, istate.time_week_ms);
@@ -536,7 +536,7 @@ uint64_t AP_GPS::last_message_epoch_usec(uint8_t instance) const
     if (istate.time_week == 0) {
         return 0;
     }
-    return time_epoch_convert(istate.time_week, drivers[instance]->get_last_itow()) * 1000ULL;
+    return time_epoch_convert(istate.time_week, drivers[instance]->get_last_itow_ms()) * 1000ULL;
 }
 
 /*
@@ -2020,7 +2020,7 @@ uint32_t AP_GPS::get_itow(uint8_t instance) const
     if (instance >= GPS_MAX_RECEIVERS || drivers[instance] == nullptr) {
         return 0;
     }
-    return drivers[instance]->get_last_itow();
+    return drivers[instance]->get_last_itow_ms();
 }
 
 bool AP_GPS::get_error_codes(uint8_t instance, uint32_t &error_codes) const
diff --git a/libraries/AP_GPS/AP_GPS_MAV.cpp b/libraries/AP_GPS/AP_GPS_MAV.cpp
index 7581c8ef33..eab22b3e50 100644
--- a/libraries/AP_GPS/AP_GPS_MAV.cpp
+++ b/libraries/AP_GPS/AP_GPS_MAV.cpp
@@ -124,7 +124,7 @@ void AP_GPS_MAV::handle_msg(const mavlink_message_t &msg)
                 state.last_corrected_gps_time_us = (corrected_ms * 1000ULL);
                 state.corrected_timestamp_updated = true;
                 if (state.last_corrected_gps_time_us) {
-                    _last_itow = state.time_week_ms;
+                    _last_itow_ms = state.time_week_ms;
                 }
                 if (have_yaw) {
                     state.gps_yaw_time_ms = corrected_ms;
diff --git a/libraries/AP_GPS/AP_GPS_UAVCAN.cpp b/libraries/AP_GPS/AP_GPS_UAVCAN.cpp
index ea57ca9ccd..ddb6205bf6 100644
--- a/libraries/AP_GPS/AP_GPS_UAVCAN.cpp
+++ b/libraries/AP_GPS/AP_GPS_UAVCAN.cpp
@@ -880,7 +880,7 @@ bool AP_GPS_UAVCAN::read(void)
             // If we were able to get a valid last_corrected_gps_time_us
             // we have had a valid GPS message time, from which we calculate
             // the time of week.
-            _last_itow = interim_state.time_week_ms;
+            _last_itow_ms = interim_state.time_week_ms;
         }
         return true;
     }
diff --git a/libraries/AP_GPS/GPS_Backend.cpp b/libraries/AP_GPS/GPS_Backend.cpp
index ea09008b94..e47ff483f2 100644
--- a/libraries/AP_GPS/GPS_Backend.cpp
+++ b/libraries/AP_GPS/GPS_Backend.cpp
@@ -235,8 +235,8 @@ void AP_GPS_Backend::set_uart_timestamp(uint16_t nbytes)
 
 void AP_GPS_Backend::check_new_itow(uint32_t itow, uint32_t msg_length)
 {
-    if (itow != _last_itow) {
-        _last_itow = itow;
+    if (itow != _last_itow_ms) {
+        _last_itow_ms = itow;
 
         /*
           we need to calculate a pseudo-itow, which copes with the
diff --git a/libraries/AP_GPS/GPS_Backend.h b/libraries/AP_GPS/GPS_Backend.h
index d0d5cda68f..937542f249 100644
--- a/libraries/AP_GPS/GPS_Backend.h
+++ b/libraries/AP_GPS/GPS_Backend.h
@@ -94,8 +94,8 @@ public:
     virtual bool get_error_codes(uint32_t &error_codes) const { return false; }
 
     // return iTOW of last message, or zero if not supported
-    uint32_t get_last_itow(void) const {
-        return (_pseudo_itow_delta_ms == 0)?(_last_itow):((_pseudo_itow/1000ULL) + _pseudo_itow_delta_ms);
+    uint32_t get_last_itow_ms(void) const {
+        return (_pseudo_itow_delta_ms == 0)?(_last_itow_ms):((_pseudo_itow/1000ULL) + _pseudo_itow_delta_ms);
     }
 
     enum DriverOptions : int16_t {
@@ -112,7 +112,7 @@ protected:
 
     uint64_t _last_pps_time_us;
     JitterCorrection jitter_correction;
-    uint32_t _last_itow;
+    uint32_t _last_itow_ms;
 
     // common utility functions
     int32_t swap_int32(int32_t v) const;