diff --git a/lib/ex_webrtc/peer_connection.ex b/lib/ex_webrtc/peer_connection.ex
index 9f1f615..ab9f4ed 100644
--- a/lib/ex_webrtc/peer_connection.ex
+++ b/lib/ex_webrtc/peer_connection.ex
@@ -198,6 +198,9 @@ defmodule ExWebRTC.PeerConnection do
 
   @doc """
   Send an RTP packet to the remote peer using specified track or its id.
+
+  Options:
+    * `rtx?` - send the packet as it was retransmited (use SSRC and payload type specific to RTX)
   """
   @spec send_rtp(
           peer_connection(),
@@ -1625,6 +1628,8 @@ defmodule ExWebRTC.PeerConnection do
       nil ->
         state
 
+      # in case NACK was received, but RTX was not negotiated
+      # as NACK and RTX are negotited independently
       {%RTPTransceiver{sender: %RTPSender{rtx_pt: nil}}, _idx} ->
         state
 
diff --git a/test/ex_webrtc/rtp_sender/nack_responder_test.exs b/test/ex_webrtc/rtp_sender/nack_responder_test.exs
index 516ef1f..194b016 100644
--- a/test/ex_webrtc/rtp_sender/nack_responder_test.exs
+++ b/test/ex_webrtc/rtp_sender/nack_responder_test.exs
@@ -24,7 +24,7 @@ defmodule ExWebRTC.RTPReceiver.NACKResponderTest do
       |> NACKResponder.record_packet(%{@packet | sequence_number: 39})
       |> NACKResponder.record_packet(%{@packet | sequence_number: 40})
 
-    nack = NACK.from_sequence_numbers(@media_ssrc, @sender_ssrc, [38, 39])
+    nack = NACK.from_sequence_numbers(@media_ssrc, @sender_ssrc, [38, 39, 237])
     {rtx_packets, nack_responder} = NACKResponder.get_rtx(nack_responder, nack)
 
     assert nack_responder.seq_no == @responder.seq_no + 2