diff --git a/clockadj.c b/clockadj.c
index 0485d8c..7b8feef 100644
--- a/clockadj.c
+++ b/clockadj.c
@@ -182,3 +182,14 @@ void sysclk_set_sync(void)
 	if (clock_adjtime(clkid, &tx) < 0)
 		pr_err("failed to set clock status and maximum error: %m");
 }
+
+void sysclk_set_unsync(void)
+{
+	clockid_t clkid = CLOCK_REALTIME;
+	struct timex tx;
+	memset(&tx, 0, sizeof(tx));
+	tx.modes = ADJ_STATUS;
+	tx.status = STA_UNSYNC;
+	if (clock_adjtime(clkid, &tx) < 0)
+		pr_err("failed to set clock status: %m");
+}
diff --git a/clockadj.h b/clockadj.h
index 4ea98c1..8a98627 100644
--- a/clockadj.h
+++ b/clockadj.h
@@ -80,4 +80,9 @@ int sysclk_max_freq(void);
  * the real-time clock (RTC) to it.
  */
 void sysclk_set_sync(void);
+
+/**
+ * Mark the system clock as unsynchronized.
+ */
+void sysclk_set_unsync(void);
 #endif
diff --git a/phc2sys.c b/phc2sys.c
index c0b7b3d..80d0b8e 100644
--- a/phc2sys.c
+++ b/phc2sys.c
@@ -735,8 +735,10 @@ static int do_loop(struct node *node, int subscriptions)
 				reconfigure(node);
 			}
 		}
-		if (!node->master)
+		if (!node->master) {
+			sysclk_set_unsync();
 			continue;
+		}
 
 		LIST_FOREACH(clock, &node->dst_clocks, dst_list) {
 			if (!update_needed(clock))