diff --git a/README.md b/README.md
index dbb1eb7..c8d63af 100644
--- a/README.md
+++ b/README.md
@@ -38,6 +38,10 @@ The following gateways are provided by this package:
 For general usage instructions, please see the main [Omnipay](https://github.com/thephpleague/omnipay)
 repository.
 
+## Quirks
+
+The transaction reference obtained from the purchase() response can't be used to refund a purchase. The transaction reference from the completePurchase() response is the one that should be used.
+
 ## Out Of Scope
 
 Omnipay does not cover recurring payments or billing agreements, and so those features are not included in this package. Extensions to this gateway are always welcome. 
diff --git a/src/Message/ExpressCompletePurchaseResponse.php b/src/Message/ExpressCompletePurchaseResponse.php
index e0ff794..551c058 100644
--- a/src/Message/ExpressCompletePurchaseResponse.php
+++ b/src/Message/ExpressCompletePurchaseResponse.php
@@ -7,14 +7,38 @@
  */
 class ExpressCompletePurchaseResponse extends ExpressAuthorizeResponse
 {
+    /*
+     * Is this complete purchase response successful? Will not be successful if it's a redirect response.
+     *
+     * @return bool
+     */
     public function isSuccessful()
     {
         $success = isset($this->data['ACK']) && in_array($this->data['ACK'], array('Success', 'SuccessWithWarning'));
         return !$this->isRedirect() && $success;
     }
 
+    /**
+     * The complete purchase response can be in error where it wants to have your customer return to paypal.
+     *
+     * @return bool
+     */
     public function isRedirect()
     {
         return isset($this->data['L_ERRORCODE0']) && in_array($this->data['L_ERRORCODE0'], array('10486'));
     }
+
+    /**
+     * The transaction reference obtained from the purchase() call can't be used to refund a purchase.
+     *
+     * @return string
+     */
+    public function getTransactionReference()
+    {
+        if ($this->isSuccessful() && isset($this->data['PAYMENTINFO_0_TRANSACTIONID'])) {
+            return $this->data['PAYMENTINFO_0_TRANSACTIONID'];
+        }
+
+        return parent::getTransactionReference();
+    }
 }