diff --git a/docs/user/security/authentication/index.asciidoc b/docs/user/security/authentication/index.asciidoc
index fe93e38151b82..30b7c071508cc 100644
--- a/docs/user/security/authentication/index.asciidoc
+++ b/docs/user/security/authentication/index.asciidoc
@@ -120,6 +120,7 @@ You can also configure both PKI and basic authentication for the same {kib} inst
 
 [source,yaml]
 --------------------------------------------------------------------------------
+server.ssl.clientAuthentication: optional
 xpack.security.authc.providers:
   pki.pki1:
     order: 0