diff --git a/server-protocol.md b/server-protocol.md
index 967862e..7005fb7 100644
--- a/server-protocol.md
+++ b/server-protocol.md
@@ -202,6 +202,10 @@ it (to avoid a race condition), but for simplicity, clients can send a claim for
 all nameplates, even ones which they've allocated themselves.
 Note that a claim (and therefore an allocation) also automatically opens the
 mailbox, see below.
+The `claim` command has the optional boolean field `dont-allocate`, which if set
+will result in an error if the to be claimed nameplate does not already exist.
+The intent behind this is clients who want to insure themselves against user
+mistakes when entering a nameplate.
 
 Nameplates (on the server) must live until the second client has learned
 about the associated mailbox, after which point they can be reused by other
@@ -302,7 +306,7 @@ any), and which ones provoke direct responses:
 * ~~S->C nameplates {nameplates: [{id: str},..]}~~ (always empty response)
 * (C->S) allocate {} -> allocated
 * S->C allocated {nameplate:}
-* (C->S) claim {nameplate:} -> claimed
+* (C->S) claim {nameplate:, dont-allocate:?bool} -> claimed
 * S->C claimed {mailbox:}
 * ~~(C->S) release {nameplate:?} -> released~~ (deprecated)
 * ~~S->C released~~