diff --git a/acqui/invoice.pl b/acqui/invoice.pl
index 3ab2d9f7c2..dd1360fd69 100755
--- a/acqui/invoice.pl
+++ b/acqui/invoice.pl
@@ -84,8 +84,8 @@ elsif ( $op && $op eq 'mod' ) {
     ModInvoice(
         invoiceid             => $invoiceid,
         invoicenumber         => $invoicenumber,
-        shipmentdate          => output_pref( { str => scalar $input->param('shipmentdate'), dateformat => 'iso', dateonly => 1 } ),
-        billingdate           => output_pref( { str => scalar $input->param('billingdate'),  dateformat => 'iso', dateonly => 1 } ),
+        shipmentdate          => scalar output_pref( { str => scalar $input->param('shipmentdate'), dateformat => 'iso', dateonly => 1 } ),
+        billingdate           => scalar output_pref( { str => scalar $input->param('billingdate'),  dateformat => 'iso', dateonly => 1 } ),
         shipmentcost          => $shipmentcost,
         shipmentcost_budgetid => $shipment_budget_id
     );