diff --git a/clock.c b/clock.c
index c5dd873..c541951 100644
--- a/clock.c
+++ b/clock.c
@@ -798,7 +798,7 @@ static void clock_forward_mgmt_msg(struct clock *c, struct port *p, struct ptp_m
 
 int clock_manage(struct clock *c, struct port *p, struct ptp_message *msg)
 {
-	int changed = 0, i;
+	int changed = 0, i, res, answers;
 	struct management_tlv *mgt;
 	struct ClockIdentity *tcid, wildcard = {
 		{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
@@ -883,9 +883,18 @@ int clock_manage(struct clock *c, struct port *p, struct ptp_message *msg)
 		clock_management_send_error(p, msg, NOT_SUPPORTED);
 		break;
 	default:
+		answers = 0;
 		for (i = 0; i < c->nports; i++) {
-			if (port_manage(c->port[i], p, msg))
-				break;
+			res = port_manage(c->port[i], p, msg);
+			if (res < 0)
+				return changed;
+			if (res > 0)
+				answers++;
+		}
+		if (!answers) {
+			/* IEEE 1588 Interpretation #21 suggests to use
+			 * WRONG_VALUE for ports that do not exist */
+			clock_management_send_error(p, msg, WRONG_VALUE);
 		}
 		break;
 	}
diff --git a/port.c b/port.c
index 390aa38..e840673 100644
--- a/port.c
+++ b/port.c
@@ -2198,11 +2198,11 @@ int port_manage(struct port *p, struct port *ingress, struct ptp_message *msg)
 	switch (management_action(msg)) {
 	case GET:
 		if (port_management_get_response(p, ingress, mgt->id, msg))
-			return 0;
+			return 1;
 		break;
 	case SET:
 		if (port_management_set(p, ingress, mgt->id, msg))
-			return 0;
+			return 1;
 		break;
 	case COMMAND:
 		break;
@@ -2234,7 +2234,7 @@ int port_manage(struct port *p, struct port *ingress, struct ptp_message *msg)
 		port_management_send_error(p, ingress, msg, NO_SUCH_ID);
 		return -1;
 	}
-	return 0;
+	return 1;
 }
 
 int port_management_error(struct PortIdentity pid, struct port *ingress,
diff --git a/port.h b/port.h
index 9d1ddc9..804e463 100644
--- a/port.h
+++ b/port.h
@@ -116,7 +116,8 @@ struct PortIdentity port_identity(struct port *p);
  * @param p        A pointer previously obtained via port_open().
  * @param ingress  The port on which 'msg' was received.
  * @param msg      A management message.
- * @return         Zero if the message is valid, non-zero otherwise.
+ * @return         1 if the message was responded to, 0 if it did not apply
+ *                 to the port, -1 if it was invalid.
  */
 int port_manage(struct port *p, struct port *ingress, struct ptp_message *msg);