diff --git a/docs/admin_api/user_admin_api.rst b/docs/admin_api/user_admin_api.rst
index 0b3d09d69403..ed6df61a26b7 100644
--- a/docs/admin_api/user_admin_api.rst
+++ b/docs/admin_api/user_admin_api.rst
@@ -2,7 +2,8 @@ Create or modify Account
 ========================
 
 This API allows an administrator to create or modify a user account with a
-specific ``user_id``.
+specific ``user_id``. Be aware that ``user_id`` is fully qualified: for example,
+``@user:server.com``.
 
 This api is::