diff --git a/frontend-backend-protocol.md b/frontend-backend-protocol.md
index 2765616..092a0f7 100644
--- a/frontend-backend-protocol.md
+++ b/frontend-backend-protocol.md
@@ -17,7 +17,8 @@ status is a one-byte value that can be either 0 (available), 1
 
 msgid is an unsigned 16 bit value that is used to identify targets of ACKs.
 You can treat it as more or less an opaque identifier that is valid at
-least as long the backend stays running.
+least as long the backend stays running or until you get another Msgid
+event with the same msgid.
 
 nick is the nick encoded as utf-8. It is allowed to have all valid Unicode
 code points other than C0 and C1 control characters and the characters