diff --git a/src/calibre/db/cache.py b/src/calibre/db/cache.py
index 5c6bd598b2..5f83b640c4 100644
--- a/src/calibre/db/cache.py
+++ b/src/calibre/db/cache.py
@@ -547,7 +547,7 @@ class Cache(object):
         '''
         af = self.fields['authors']
         if author_ids is None:
-            author_ids = tuple(af.table.id_map)
+            return {aid:af.author_data(aid) for aid in af.table.id_map}
         return {aid:af.author_data(aid) for aid in author_ids if aid in af.table.id_map}
 
     @read_api