diff --git a/stockcli/books.py b/stockcli/books.py
--- a/stockcli/books.py
+++ b/stockcli/books.py
@@ -28,6 +28,10 @@ def add_book_by_barcode(barcode: str) ->
         book_metadata = utils.get_request(
             f"userfields/userentity-books/{book['id']}", cached=True
         )
+
+        if book_metadata["isbn"] is None:
+            continue
+
         if isbnlib.canonical(book_metadata["isbn"]) == canonical_isbn:
 
             book_metadata = utils.get_request(