diff --git a/Changelog.md b/Changelog.md
index 18676d969..6c708a957 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -6,6 +6,7 @@
 - Rename `quic.Cookie` to `quic.Token` and `quic.Config.AcceptCookie` to `quic.Config.AcceptToken`.
 - Distinguish between Retry tokens and tokens sent in NEW_TOKEN frames.
 - Enforce application protocol negotiation (via `tls.Config.NextProtos`).
+- Use a varint for error codes.
 
 ## v0.11.0 (2019-04-05)
 
diff --git a/interface.go b/interface.go
index 768e5fe13..9a7e1fbaa 100644
--- a/interface.go
+++ b/interface.go
@@ -27,6 +27,7 @@ type Token struct {
 }
 
 // An ErrorCode is an application-defined error code.
+// Valid values range between 0 and MAX_UINT62.
 type ErrorCode = protocol.ApplicationErrorCode
 
 // Stream is the interface implemented by QUIC streams