diff --git a/lib/books.ts b/lib/books.ts
index 252ac27..cd4a8ed 100644
--- a/lib/books.ts
+++ b/lib/books.ts
@@ -40,7 +40,7 @@ export async function getBook(id: number): Promise<DetailedBook> {
 export interface DetailedBook {
   isbn: string | null;
   lccn: string | null;
-  title: string;
+  title: string | null;
   authors: string | null;
   edition: string | null;
   publisher: string | null;