diff --git a/apps/readest-app/src/utils/lang.ts b/apps/readest-app/src/utils/lang.ts
index fcd9eb3a..82d144ab 100644
--- a/apps/readest-app/src/utils/lang.ts
+++ b/apps/readest-app/src/utils/lang.ts
@@ -89,6 +89,7 @@ export const isSameLang = (lang1?: string | null, lang2?: string | null): boolea
 export const isValidLang = (lang?: string) => {
   if (!lang) return false;
   if (typeof lang !== 'string') return false;
+  if (['und', 'mul', 'mis', 'zxx'].includes(lang)) return false;
   const code = normalizedLangCode(lang);
   return iso6392.some((l) => l.iso6391 === code || l.iso6392B === code);
 };