diff --git a/ajax/convertWithSign.php b/ajax/convertWithSign.php
index f7bb2e643abf445b13120af0f526195d4ee4f5fc..3ba06664741f0ff09bb82f8d264faa5c5f0b3d14 100644
--- a/ajax/convertWithSign.php
+++ b/ajax/convertWithSign.php
@@ -18,6 +18,10 @@ function ($data) {
         $data = json_decode($data, true);
         $result = [];
 
+        if (!class_exists('QUI\ERP\Money\Price')) {
+            return $result;
+        }
+
         foreach ($data as $entry) {
             $amount = $entry['amount'];
             $currencyFrom = $entry['from'];