diff --git a/APPL/FIN/fin_edit_factuur_save.asp b/APPL/FIN/fin_edit_factuur_save.asp
index 5c793d1c02..0a2bb56f65 100644
--- a/APPL/FIN/fin_edit_factuur_save.asp
+++ b/APPL/FIN/fin_edit_factuur_save.asp
@@ -25,7 +25,7 @@ FCLTHeader.Requires({ js:[] })
 
 var fin_key = getFParamInt("fin_key", -1);
 var fin_type = getFParam("fin_type", -1);
-var referentienr = getFParam("referentienr", -1);
+var referentienr = getFParam("referentienr", "-1");
 var fin_status_key = getFParamInt("fin_status_key", -1);
 var copyfin_key = getFParamInt("copyfin_key", -1);