diff --git a/rrlp-ephemeris/gps.h b/rrlp-ephemeris/gps.h
index 03d643f..241b9d7 100644
--- a/rrlp-ephemeris/gps.h
+++ b/rrlp-ephemeris/gps.h
@@ -151,12 +151,20 @@
 };
 
 
+/* Reference time */
+struct gps_ref_time {
+	int wn;			/* GPS week number */
+	double tow;		/* in seconds */
+};
+
+
 /* All assist data */
 #define GPS_FIELD_IONOSPHERE	(1<<0)
 #define GPS_FIELD_UTC		(1<<1)
 #define GPS_FIELD_ALMANAC	(1<<2)
 #define GPS_FIELD_EPHEMERIS	(1<<3)
 #define GPS_FIELD_REFPOS	(1<<4)
+#define GPS_FIELD_REFTIME	(1<<5)
 
 struct gps_assist_data {
 	int fields;
@@ -165,6 +173,7 @@
 	struct gps_almanac		almanac;
 	struct gps_ephemeris		ephemeris;
 	struct gps_ref_pos		ref_pos;
+	struct gps_ref_time		ref_time;
 };