Index: src/wp-includes/ms-functions.php
===================================================================
--- src/wp-includes/ms-functions.php	(revision 29830)
+++ src/wp-includes/ms-functions.php	(working copy)
@@ -1379,7 +1379,8 @@
 	make_db_current_silent( 'blog' );
 	populate_options();
 	populate_roles();
-	$wp_roles->_init();
+	unset( $wp_roles );
+	$wp_roles = new WP_Roles();
 
 	$url = untrailingslashit( $url );