diff --git a/api/v3/TwingleDonation/Endrecurring.php b/api/v3/TwingleDonation/Endrecurring.php
index 005b6c9..83f20e0 100644
--- a/api/v3/TwingleDonation/Endrecurring.php
+++ b/api/v3/TwingleDonation/Endrecurring.php
@@ -87,6 +87,16 @@ function civicrm_api3_twingle_donation_endrecurring($params) {
         time(),
         date_create_from_format('Ymd', $params['cancelled_at'])->getTimestamp()
       ));
+
+      // verify that the mandate has not been terminated in the past
+      $mandate_status = civicrm_api3('SepaMandate', 'getvalue', ['return' => 'status', 'id' => $mandate_id]);
+      if ($mandate_status != 'FRST' && $mandate_status != 'RCUR') {
+        throw new CiviCRM_API3_Exception(
+            E::ts("SEPA Mandate [%1] already terminated.", [1 => $mandate_id]),
+            'api_error'
+        );
+      }
+
       if (!CRM_Sepa_BAO_SEPAMandate::terminateMandate(
         $mandate_id,
         $end_date,