diff --git a/wp-admin/includes/class-wp-upgrader.php b/wp-admin/includes/class-wp-upgrader.php
index 7c8e94c045..6e16bd1537 100644
--- a/wp-admin/includes/class-wp-upgrader.php
+++ b/wp-admin/includes/class-wp-upgrader.php
@@ -190,6 +190,7 @@ class WP_Upgrader {
 		);
 
 		$args = wp_parse_args($args, $defaults);
+		$source = $args['source'];
 		$destination = $args['destination'];
 		$clear_destination = $args['clear_destination'];