diff --git a/app/Helpers/Collector/GroupCollector.php b/app/Helpers/Collector/GroupCollector.php
index 060da5eee1..358914c74a 100644
--- a/app/Helpers/Collector/GroupCollector.php
+++ b/app/Helpers/Collector/GroupCollector.php
@@ -506,7 +506,7 @@ class GroupCollector implements GroupCollectorInterface
                     $groups[$groudId]['sums'][$currencyId]['currency_decimal_places'] = $transaction['currency_decimal_places'];
                     $groups[$groudId]['sums'][$currencyId]['amount']                  = '0';
                 }
-                $groups[$groudId]['sums'][$currencyId]['amount'] = bcadd($groups[$groudId]['sums'][$currencyId]['amount'], $transaction['amount'] ?? '0');
+                $groups[$groudId]['sums'][$currencyId]['amount'] = bcadd($groups[$groudId]['sums'][$currencyId]['amount'], (string)($transaction['amount'] ?? '0'));
 
                 if (null !== $transaction['foreign_amount'] && null !== $transaction['foreign_currency_id']) {
                     $currencyId = (int) $transaction['foreign_currency_id'];