diff --git a/partner-masterpulsa-voucher.js b/partner-masterpulsa-voucher.js
index cba6914..67312c4 100644
--- a/partner-masterpulsa-voucher.js
+++ b/partner-masterpulsa-voucher.js
@@ -138,6 +138,10 @@ function parsePaymentResponse(message) {
             retval.sn = data[9];
         }
         catch(err) {
+            retval.sn = null;
+        }
+
+        if (!retval.sn) {
             retval.sn = rehashRefnum(retval.refnum);
         }
     }