diff --git a/src/DataGroup/Element/PaymentReference.php b/src/DataGroup/Element/PaymentReference.php
index 2209e174..6a35ca49 100644
--- a/src/DataGroup/Element/PaymentReference.php
+++ b/src/DataGroup/Element/PaymentReference.php
@@ -30,7 +30,7 @@ class PaymentReference implements GroupSequenceProviderInterface, QrCodeableInte
      * Structured reference number
      * Either a QR reference or a Creditor Reference (ISO 11649)
      *
-     * @var string
+     * @var string|null
      */
     private $reference;