diff --git a/module/finc/src/finc/ILS/Driver/FincILS.php b/module/finc/src/finc/ILS/Driver/FincILS.php
index 4dbb8c94e4b9546cae0e9e32304a6b741760f398..6a204440bdc41f2122b145e283d04b7763521c23 100644
--- a/module/finc/src/finc/ILS/Driver/FincILS.php
+++ b/module/finc/src/finc/ILS/Driver/FincILS.php
@@ -421,7 +421,7 @@ class FincILS extends PAIA implements LoggerAwareInterface
                 $retval = array_fill(0, count($ids), false);
                 foreach ($new['first_results'] as $record) {
                     /** @var \finc\RecordDriver\SolrDefault $record */
-                    $callNumbers = $record->getField($idType);
+                    $callNumbers = (array)$record->getField($idType);
                     $matches = array_intersect($ids, $callNumbers);
                     foreach ($matches as $number => $match) {
                         /* map identifier to solr id */