diff --git a/app/src/Controller/TierApiController.php b/app/src/Controller/TierApiController.php
index 4003384df..56d9253c9 100644
--- a/app/src/Controller/TierApiController.php
+++ b/app/src/Controller/TierApiController.php
@@ -280,7 +280,7 @@ protected function doMatchRequest(bool $searchOnly=false) {
             if(!$searchOnly) {
               // This should also correctly handle an update match attribute request
               // that did not originally have a referenceid
-              $MatchService->attachReferenceId($sor, $sorid, $AttributeManager, $refIds[0]);
+              $MatchService->attachReferenceId($sor, $sorid, $AttributeManager, (string)$refIds[0]);
             }
             
             $result = ['referenceId' => $refIds[0]];