diff --git a/specification/10_client_server_api.rst b/specification/10_client_server_api.rst
index 0d7d06d5..17eca502 100644
--- a/specification/10_client_server_api.rst
+++ b/specification/10_client_server_api.rst
@@ -1019,6 +1019,9 @@ username
   Home Server must generate a Matrix ID local part.
 password
   Required. The desired password for the account.
+bind_email
+  Optional. If ``true``, the server binds the email used for authentication to
+  the Matrix ID with the ID Server.
 
 On success, this returns a JSON object with keys: