diff --git a/class.paperless.php b/class.paperless.php
index 552e82a..460ac50 100644
--- a/class.paperless.php
+++ b/class.paperless.php
@@ -111,7 +111,7 @@ class SeedDMS_ExtPaperless_RestAPI_Controller { /* {{{ */
 			'created_date'=>date('Y-m-d', $document->getDate()),
 			'modified'=>date('Y-m-d\TH:i:s+02:00', $document->getDate()),
 			'added'=>date('Y-m-d\TH:i:s+02:00', $document->getDate()),
-			'archive_serial_number'=>null,
+			'archive_serial_number'=> (int) $document->getId(), // was null
 			'original_file_name'=>$lc->getOriginalFileName(),
 			'archived_file_name'=>$lc->getOriginalFileName()
 		);