Index: wp-includes/class-wp-xmlrpc-server.php
===================================================================
--- wp-includes/class-wp-xmlrpc-server.php	(revision 21081)
+++ wp-includes/class-wp-xmlrpc-server.php	(working copy)
@@ -2194,7 +2194,7 @@
 		do_action('xmlrpc_call', 'wp.getAuthors');
 
 		$authors = array();
-		foreach ( get_users( array( 'fields' => array('ID','user_login','display_name') ) ) as $user ) {
+		foreach ( get_users( array( 'fields' => array('ID','user_login','display_name'), 'who' => 'authors' ) ) as $user ) {
 			$authors[] = array(
 				'user_id'       => $user->ID,
 				'user_login'    => $user->user_login,