diff --git a/src/calibre/ebooks/metadata/meta.py b/src/calibre/ebooks/metadata/meta.py
index 7c89a9bc0d..28dcbf5ae0 100644
--- a/src/calibre/ebooks/metadata/meta.py
+++ b/src/calibre/ebooks/metadata/meta.py
@@ -31,7 +31,7 @@ def metadata_from_formats(formats):
     try:
         return _metadata_from_formats(formats)
     except:
-        mi = metadata_from_filename(list(formats)[0])
+        mi = metadata_from_filename(list(iter(formats))[0])
         if not mi.authors:
             mi.authors = [_('Unknown')]
 
diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 18765e3e3c..149e92ddf9 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -1764,7 +1764,7 @@ books_series_link      feeds
         formats = self.find_books_in_directory(dirpath, True)
         if not formats:
             return
-        formats = list(formats)
+        formats = list(iter(formats))
         mi = metadata_from_formats(formats)
         if mi.title is None:
             return