diff --git a/x-pack/docs/en/security/authentication/file-realm.asciidoc b/x-pack/docs/en/security/authentication/file-realm.asciidoc
index 010c5348008..5d9e04a3274 100644
--- a/x-pack/docs/en/security/authentication/file-realm.asciidoc
+++ b/x-pack/docs/en/security/authentication/file-realm.asciidoc
@@ -21,7 +21,8 @@ credentials of all other users.
 
 IMPORTANT: When you configure realms in `elasticsearch.yml`, only the realms you
 specify are used for authentication. To use the `file` realm you must explicitly
-include it in the realm chain.
+include it in the realm chain. While it is possible to define multiple instances
+of some other realms, you can define only _one_ file realm per node.
 
 To define users, the {security-features} provide the
 {ref}/users-command.html[users] command-line tool. This tool enables you to add