diff --git a/port.c b/port.c
index 6104061..48fff1c 100644
--- a/port.c
+++ b/port.c
@@ -2737,8 +2737,10 @@ int port_forward_to(struct port *p, struct ptp_message *msg)
 {
 	int cnt;
 	cnt = transport_sendto(p->trp, &p->fda, TRANS_GENERAL, msg);
-	if (cnt <= 0) {
-		return -1;
+	if (cnt < 0) {
+		return cnt;
+	} else if (!cnt) {
+		return -EIO;
 	}
 	port_stats_inc_tx(p, msg);
 	return 0;
diff --git a/port.h b/port.h
index a45a7a4..e347e36 100644
--- a/port.h
+++ b/port.h
@@ -94,7 +94,7 @@ int port_forward(struct port *p, struct ptp_message *msg);
  * Forward a message on a given port to the address stored in the message.
  * @param port    A pointer previously obtained via port_open().
  * @param msg     The message to send. Must be in network byte order.
- * @return        Zero on success, non-zero otherwise.
+ * @return        Zero on success, negative errno value otherwise.
  */
 int port_forward_to(struct port *p, struct ptp_message *msg);