diff --git a/draft-ietf-quic-transport.md b/draft-ietf-quic-transport.md
index ca4e57051c..d08fa38cbc 100644
--- a/draft-ietf-quic-transport.md
+++ b/draft-ietf-quic-transport.md
@@ -5390,7 +5390,7 @@ Sequence Number:
   {{retiring-cids}}.
 
 Receipt of a RETIRE_CONNECTION_ID frame containing a sequence number greater
-than any previously sent to the peer MAY be treated as a connection error of
+than any previously sent to the peer MUST be treated as a connection error of
 type PROTOCOL_VIOLATION.
 
 The sequence number specified in a RETIRE_CONNECTION_ID frame MUST NOT refer