diff --git a/src/calibre/devices/usbms/books.py b/src/calibre/devices/usbms/books.py
index bcc910282b..441efc0424 100644
--- a/src/calibre/devices/usbms/books.py
+++ b/src/calibre/devices/usbms/books.py
@@ -73,7 +73,7 @@ class BookList(_BookList):
         return False
 
     def add_book(self, book, replace_metadata):
-        self.add_book_extended(book, replace_metadata, check_for_duplicates=True)
+        return self.add_book_extended(book, replace_metadata, check_for_duplicates=True)
 
     def add_book_extended(self, book, replace_metadata, check_for_duplicates):
         '''