diff --git a/clock.c b/clock.c
index 274a6a0..ea2d97e 100644
--- a/clock.c
+++ b/clock.c
@@ -79,6 +79,7 @@ struct clock {
 	int utc_timescale;
 	int leap_set;
 	int kernel_leap;
+	int time_source; /* grand master role */
 	enum servo_state servo_state;
 	tmv_t master_offset;
 	tmv_t path_delay;
@@ -436,7 +437,7 @@ static void clock_update_grandmaster(struct clock *c)
 	} else {
 		c->tds.flags = PTP_TIMESCALE;
 	}
-	c->tds.timeSource                       = INTERNAL_OSCILLATOR;
+	c->tds.timeSource                       = c->time_source;
 }
 
 static void clock_update_slave(struct clock *c)
@@ -570,6 +571,7 @@ struct clock *clock_create(int phc_index, struct interface *iface, int count,
 	c->free_running = dds->free_running;
 	c->freq_est_interval = dds->freq_est_interval;
 	c->kernel_leap = dds->kernel_leap;
+	c->time_source = dds->time_source;
 	c->desc = dds->clock_desc;
 
 	if (c->free_running) {
diff --git a/ds.h b/ds.h
index f653aee..9977e40 100644
--- a/ds.h
+++ b/ds.h
@@ -54,6 +54,7 @@ struct default_ds {
 	int freq_est_interval; /*log seconds*/
 	int stats_interval; /*log seconds*/
 	int kernel_leap;
+	int time_source;
 	struct clock_description clock_desc;
 };
 
diff --git a/ptp4l.c b/ptp4l.c
index 1e0304e..632166c 100644
--- a/ptp4l.c
+++ b/ptp4l.c
@@ -54,6 +54,7 @@ static struct config cfg_settings = {
 		.freq_est_interval = 1,
 		.stats_interval = 0,
 		.kernel_leap = 1,
+		.time_source = INTERNAL_OSCILLATOR,
 		.clock_desc = {
 			.productDescription = {
 				.max_symbols = 64,