Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 12317)
+++ wp-includes/user.php	(working copy)
@@ -518,8 +518,7 @@
 	$r = wp_parse_args( $args, $defaults );
 	extract( $r, EXTR_SKIP );
 
-	$query = "SELECT * FROM $wpdb->users";
-
+	$query = "SELECT {$wpdb->users}.* FROM $wpdb->users, $wpdb->usermeta";
 	$query_where = array();
 
 	if ( is_array($include) )
@@ -534,8 +533,9 @@
 	if ( $exclude )
 		$query_where[] = "ID NOT IN ($exclude)";
 
+	$query .= " WHERE {$wpdb->users}.ID = {$wpdb->usermeta}.user_id AND meta_key = '{$wpdb->prefix}capabilities'"
 	if ( $query_where )
-		$query .= " WHERE " . join(' AND', $query_where);
+		$query .= " AND " . join(' AND', $query_where);
 
 	$query .= " ORDER BY $orderby $order";