diff --git a/src/wp-admin/includes/upgrade.php b/src/wp-admin/includes/upgrade.php
index 0c7c1ecccd..b2354a7940 100644
--- a/src/wp-admin/includes/upgrade.php
+++ b/src/wp-admin/includes/upgrade.php
@@ -556,6 +556,7 @@ function upgrade_100() {
 
 	$done_ids = $wpdb->get_results("SELECT DISTINCT post_id FROM $wpdb->post2cat");
 	if ($done_ids) :
+		$done_posts = array();
 		foreach ($done_ids as $done_id) :
 			$done_posts[] = $done_id->post_id;
 		endforeach;