Index: wp-admin/includes/update-core.php
===================================================================
--- wp-admin/includes/update-core.php	(revision 11559)
+++ wp-admin/includes/update-core.php	(working copy)
@@ -229,7 +229,7 @@
 	$result = copy_dir($from . '/wordpress', $to);
 	if ( is_wp_error($result) ) {
 		$wp_filesystem->delete($maintenance_file);
-		$wp_filesystem->delete($working_dir, true);
+		$wp_filesystem->delete($from, true);
 		return $result;
 	}