diff --git a/draft-ietf-quic-http.md b/draft-ietf-quic-http.md
index 138eb269ef..48490e0f26 100644
--- a/draft-ietf-quic-http.md
+++ b/draft-ietf-quic-http.md
@@ -1394,6 +1394,11 @@ the entire connection when an error is encountered.  These are referred to as
 {{QUIC-TRANSPORT}}.  An endpoint MAY choose to treat a stream error as a
 connection error.
 
+Because new error codes can be defined without negotiation (see {{extensions}}),
+receipt of an unknown error code or use of an error code in an unexpected
+context MUST NOT be treated as an error.  However, closing a stream can
+constitute an error regardless of the error code (see {{request-response}}).
+
 This section describes HTTP/3-specific error codes which can be used to express
 the cause of a connection or stream error.