diff --git a/content/client-server-api/_index.md b/content/client-server-api/_index.md
index f6bc6580..bf0bd704 100644
--- a/content/client-server-api/_index.md
+++ b/content/client-server-api/_index.md
@@ -246,10 +246,6 @@ particular domain.
 : The third party identifier specified by the client is not acceptable because it is
 already in use in some way.
 
-`M_THREEPID_IN_USE`
-: Sent when a threepid given to an API cannot be used because the same
-threepid is already in use.
-
 `M_THREEPID_MEDIUM_NOT_SUPPORTED`
 : The homeserver does not support adding a third party identifier of the given medium.