diff --git a/module/VuFind/src/VuFind/Hierarchy/TreeRenderer/JSTree.php b/module/VuFind/src/VuFind/Hierarchy/TreeRenderer/JSTree.php
index e2e635e2818ae65e0c8649701d8ede6ec781f48c..99394d18fc306dbbe7ecba0f471ca60b847c669f 100644
--- a/module/VuFind/src/VuFind/Hierarchy/TreeRenderer/JSTree.php
+++ b/module/VuFind/src/VuFind/Hierarchy/TreeRenderer/JSTree.php
@@ -92,7 +92,8 @@ class JSTree extends AbstractBase
             $hierarchies = [];
             foreach ($inHierarchies as $hierarchyTopID) {
                 if ($this->getDataSource()->supports($hierarchyTopID)) {
-                    $hierarchies[$hierarchyTopID] = $inHierarchiesTitle[$i];
+                    $hierarchies[$hierarchyTopID] = isset($inHierarchiesTitle[$i])
+                        ? $inHierarchiesTitle[$i] : '';
                 }
                 $i++;
             }