diff --git a/msg.h b/msg.h
index c28dd0b..f479e9c 100644
--- a/msg.h
+++ b/msg.h
@@ -212,6 +212,17 @@ static inline Boolean field_is_set(struct ptp_message *m, int index, Octet bit)
 	return m->header.flagField[index] & bit ? TRUE : FALSE;
 }
 
+/**
+ * Obtain the transportSpecific field from a message.
+ * @param m  Message to test.
+ * @return   The value of the transportSpecific field. Note that the
+ *           value is returned unshifted, in the upper nibble.
+ */
+static inline UInteger8 msg_transport_specific(struct ptp_message *m)
+{
+	return m->header.tsmt & 0xf0;
+}
+
 /**
  * Obtain the message type.
  * @param m  Message to test.
diff --git a/port.c b/port.c
index e2fe9cc..910ecee 100644
--- a/port.c
+++ b/port.c
@@ -290,6 +290,9 @@ static int port_ignore(struct port *p, struct ptp_message *m)
 {
 	struct ClockIdentity c1, c2;
 
+	if (msg_transport_specific(m) != p->transportSpecific) {
+		return 1;
+	}
 	if (pid_eq(&m->header.sourcePortIdentity, &p->portIdentity)) {
 		return 1;
 	}