diff --git a/userscript/novel-bookmark.user.js b/userscript/novel-bookmark.user.js
index 847647e..8f75a3e 100644
--- a/userscript/novel-bookmark.user.js
+++ b/userscript/novel-bookmark.user.js
@@ -862,7 +862,7 @@
     // before the due filter records no freshness timestamp and consumes no
     // per-navigation batch slot.
     const adapter = adapterFor(site);
-    if (!adapter.latestChapterFromAnchors) return;
+    if (!adapter || !adapter.latestChapterFromAnchors) return;
 
     const checked = loadLastChecked();
     const now = Date.now();