Grammar

Author: martinthomson

draft-ietf-quic-transport.md

@@ -3892,7 +3892,7 @@ packets with ACK frames.
 
 ## Opportunistic ACK Attack
 
-An endpoint that acknowledges packets they have not received might cause a
+An endpoint that acknowledges packets it has not received might cause a
 congestion controller to permit sending at rates beyond what the network
 supports.  An endpoint MAY skip packet numbers when sending packets to detect
 this.  An endpoint can then drop connection state and stop sending packets