diff --git a/man/mosquitto.conf.5.xml b/man/mosquitto.conf.5.xml
index 4121a8d4..35e016c8 100644
--- a/man/mosquitto.conf.5.xml
+++ b/man/mosquitto.conf.5.xml
@@ -1263,6 +1263,7 @@ log_timestamp_format %Y-%m-%dT%H:%M:%S
 							disconnected as not authorised when this option is
 							set to true. Do not use in conjunction with
 							<option>clientid_prefixes</option>.</para>
+						<para>This does not apply globally, but on a per-listener basis.</para>
 						<para>See also
 							<option>use_identity_as_username</option>.</para>
 						<para>Not reloaded on reload signal.</para>
diff --git a/mosquitto.conf b/mosquitto.conf
index 8da8a59e..10b0406e 100644
--- a/mosquitto.conf
+++ b/mosquitto.conf
@@ -290,6 +290,7 @@
 # authorised when this option is set to true.
 # Do not use in conjunction with clientid_prefixes.
 # See also use_identity_as_username.
+# This does not apply globally, but on a per-listener basis.
 #use_username_as_clientid
 
 # Change the websockets headers size. This is a global option, it is not