diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index d6362f2a76..d01c943fce 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -3739,7 +3739,7 @@ books_series_link      feeds
                 if not ext:
                     continue
                 ext = ext[1:].lower()
-                if ext not in BOOK_EXTENSIONS and ext != 'opf':
+                if ext not in BOOK_EXTENSIONS:
                     continue
 
                 key = os.path.splitext(path)[0]