diff --git a/src/components/TocList.vue b/src/components/TocList.vue
index 469b1a9e..c564daa8 100644
--- a/src/components/TocList.vue
+++ b/src/components/TocList.vue
@@ -20,7 +20,7 @@ export default {
 			// Auto-expand a single top-level structure with children
 			expandedStructures: this.level === 0
 				&& this.structures.length === 1
-				&& this.structures[0].items.some((item) => item.items)
+				&& this.structures[0].items?.some((item) => item.items)
 				? [true]
 				: [],
 			id: this.$store.getId(`toc-list-${Math.floor(Math.random() * 1e12)}`),
diff --git a/src/plugins/store.js b/src/plugins/store.js
index 77eba3c2..469ad328 100644
--- a/src/plugins/store.js
+++ b/src/plugins/store.js
@@ -133,7 +133,7 @@ function Store(args) {
 
 			if (store.manifest.structures.some((structure) => structure.type === 'Range')) {
 				return store.manifest.structures.length === 1 && store.manifest.structures[0].behavior?.includes('top')
-					? store.manifest.structures[0].items
+					? (store.manifest.structures[0].items || [])
 					: store.manifest.structures;
 			}