Index: src/wp-admin/includes/ajax-actions.php
===================================================================
--- src/wp-admin/includes/ajax-actions.php	(revision 39548)
+++ src/wp-admin/includes/ajax-actions.php	(working copy)
@@ -246,7 +246,7 @@
 		wp_die( -1 );
 
 	/** This filter is documented in wp-admin/user-new.php */
-	if ( ! is_super_admin() && ! apply_filters( 'autocomplete_users_for_site_admins', false ) )
+	if ( ! current_user_can( 'manage_network_users' ) && ! apply_filters( 'autocomplete_users_for_site_admins', false ) )
 		wp_die( -1 );
 
 	$return = array();
Index: src/wp-admin/user-new.php
===================================================================
--- src/wp-admin/user-new.php	(revision 39548)
+++ src/wp-admin/user-new.php	(working copy)
@@ -225,7 +225,7 @@
  * @param bool $enable Whether to enable auto-complete for non-super admins. Default false.
  */
 if ( is_multisite() && current_user_can( 'promote_users' ) && ! wp_is_large_network( 'users' )
-	&& ( is_super_admin() || apply_filters( 'autocomplete_users_for_site_admins', false ) )
+	&& ( current_user_can( 'manage_network_users' ) || apply_filters( 'autocomplete_users_for_site_admins', false ) )
 ) {
 	wp_enqueue_script( 'user-suggest' );
 }