diff --git a/module/VuFind/src/VuFind/ILS/Driver/Sierra.php b/module/VuFind/src/VuFind/ILS/Driver/Sierra.php
index 0f4ea099fdba6e3a721ba65d54c1bd36dafe3fe8..1fc8b27302c97dc4f99bc7c8526813074802e302 100644
--- a/module/VuFind/src/VuFind/ILS/Driver/Sierra.php
+++ b/module/VuFind/src/VuFind/ILS/Driver/Sierra.php
@@ -494,6 +494,7 @@ class Sierra extends AbstractBase implements TranslatorAwareInterface
             foreach ($itemIds as $item) {
                 $callnumber = null;
                 $results1 = pg_execute($this->db, "prep_query", [$item]);
+                $number = "";
                 while ($row1 = pg_fetch_row($results1)) {
                     if ($row1[4] == "b") {
                         $barcode = $row1[3];