diff --git a/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c b/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c
index 0958a59887..9455c26bde 100644
--- a/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c
+++ b/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c
@@ -702,6 +702,8 @@ tftp_state _tftp_state_processes(tftp_context_t *ctxt, msg_t *m)
 
             if (proc == TS_DUP) {
                 DEBUG("tftp: duplicated data received, acking...\n");
+                ctxt->dst_port = byteorder_ntohs(udp->src_port);
+                DEBUG("tftp: client's port is %" PRIu16 "\n", ctxt->dst_port);
                 _tftp_send_dack(ctxt, outbuf, TO_ACK);
                 return TS_BUSY;
             }