diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 0b1182c0bf..50b404b4be 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -1781,7 +1781,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
             path_changed = True
         if set_authors:
             if not mi.authors:
-                    mi.authors = [_('Unknown')]
+                mi.authors = [_('Unknown')]
             authors = []
             for a in mi.authors:
                 authors += string_to_authors(a)