diff --git a/libraries/AP_GPS/AP_GPS_UBLOX.cpp b/libraries/AP_GPS/AP_GPS_UBLOX.cpp
index 63b142b861..44f32992ef 100644
--- a/libraries/AP_GPS/AP_GPS_UBLOX.cpp
+++ b/libraries/AP_GPS/AP_GPS_UBLOX.cpp
@@ -1335,8 +1335,10 @@ static const char *reasons[] = {"navigation rate",
                                 "navigation settings",
                                 "GNSS settings",
                                 "SBAS settings",
-                                "PVT rate"};
+                                "PVT rate",
+                                "time pulse settings"};
 
+static_assert((1 << ARRAY_SIZE(reasons)) == CONFIG_LAST, "UBLOX: Missing configuration description");
 
 void
 AP_GPS_UBLOX::broadcast_configuration_failure_reason(void) const {
diff --git a/libraries/AP_GPS/AP_GPS_UBLOX.h b/libraries/AP_GPS/AP_GPS_UBLOX.h
index 5d8fbce19e..3a74fdebb9 100644
--- a/libraries/AP_GPS/AP_GPS_UBLOX.h
+++ b/libraries/AP_GPS/AP_GPS_UBLOX.h
@@ -73,6 +73,7 @@
 #define CONFIG_SBAS          (1<<12)
 #define CONFIG_RATE_PVT      (1<<13)
 #define CONFIG_TP5           (1<<14)
+#define CONFIG_LAST          (1<<15) // this must always be the last bit
 
 #define CONFIG_REQUIRED_INITIAL (CONFIG_RATE_NAV | CONFIG_RATE_POSLLH | CONFIG_RATE_STATUS | CONFIG_RATE_VELNED)