diff --git a/doc/arm/plugins.inc.rst b/doc/arm/plugins.inc.rst
index 7e63995f3a..4a89efdb9e 100644
--- a/doc/arm/plugins.inc.rst
+++ b/doc/arm/plugins.inc.rst
@@ -47,8 +47,10 @@ A plugin is configured with the :any:`plugin` statement in :iscman:`named.conf`:
        };
 
 
-In this example, file ``library.so`` is the plugin library. ``query``
-indicates that this is a query plugin.
+In this example, ``query`` indicates that this is a query plugin,
+and ``library.so`` is the name of the plugin library.  Note that the
+library file extension (in this case, ``.so``) is optional, and can
+be omitted.
 
 Multiple :any:`plugin` statements can be specified, to load different
 plugins or multiple instances of the same plugin.