diff --git a/draft-ietf-quic-recovery.md b/draft-ietf-quic-recovery.md
index 2cb673208b..8da067a3d8 100644
--- a/draft-ietf-quic-recovery.md
+++ b/draft-ietf-quic-recovery.md
@@ -496,6 +496,13 @@ MAY use alternate strategies for determining the content of probe packets,
 including sending new or retransmitted data based on the application's
 priorities.
 
+When a PTO timer expires, new or previously-sent data may not be available to
+send and packets may still be in flight.  A sender can be blocked from sending
+new data in the future if packets are left in flight.  Under these conditions, a
+sender SHOULD mark any packets still in flight as lost.  If a sender wishes to
+establish delivery of packets still in flight, it MAY send an ack-eliciting
+packet and re-arm the PTO timer instead.
+
 
 #### Loss Detection {#pto-loss}