diff --git a/bacnet-stack/ports/stm32f10x/dlmstp.c b/bacnet-stack/ports/stm32f10x/dlmstp.c
index 8b212ec4..7879f9bf 100644
--- a/bacnet-stack/ports/stm32f10x/dlmstp.c
+++ b/bacnet-stack/ports/stm32f10x/dlmstp.c
@@ -1281,7 +1281,11 @@ int dlmstp_send_pdu(
             pkt->buffer[i] = pdu[i];
         }
         pkt->length = pdu_len;
-        pkt->destination_mac = dest->mac[0];
+        if (dest->mac_len == 0) {
+            pkt->destination_mac = MSTP_BROADCAST_ADDRESS;
+        } else {
+            pkt->destination_mac = dest->mac[0];
+        }
         bytes_sent = pdu_len;
     }