diff --git a/clock.c b/clock.c
index 219436f..7ef2852 100644
--- a/clock.c
+++ b/clock.c
@@ -320,10 +320,6 @@ static int clock_management_set(struct clock *c, struct port *p,
 
 	switch (id) {
 	case GRANDMASTER_SETTINGS_NP:
-		if (p != c->port[c->nports]) {
-			/* Sorry, only allowed on the UDS port. */
-			break;
-		}
 		gsn = (struct grandmaster_settings_np *) tlv->data;
 		c->dds.clockQuality = gsn->clockQuality;
 		c->utc_offset = gsn->utc_offset;
@@ -843,6 +839,11 @@ int clock_manage(struct clock *c, struct port *p, struct ptp_message *msg)
 			clock_management_send_error(p, msg, WRONG_LENGTH);
 			return changed;
 		}
+		if (p != c->port[c->nports]) {
+			/* Sorry, only allowed on the UDS port. */
+			clock_management_send_error(p, msg, NOT_SUPPORTED);
+			return changed;
+		}
 		if (clock_management_set(c, p, mgt->id, msg, &changed))
 			return changed;
 		break;