diff --git a/src/calibre/ebooks/metadata/__init__.py b/src/calibre/ebooks/metadata/__init__.py
index 2f14441faa..2ca67e526d 100644
--- a/src/calibre/ebooks/metadata/__init__.py
+++ b/src/calibre/ebooks/metadata/__init__.py
@@ -38,7 +38,7 @@ class MetaInformation(object):
                 setattr(ans, attr, getattr(mi, attr))
         
     
-    def __init__(self, title, authors=['Unknown']):
+    def __init__(self, title, authors=[_('Unknown')]):
         '''
         @param title: title or "Unknown" or a MetaInformation object
         @param authors: List of strings or []
diff --git a/src/calibre/ebooks/metadata/opf.py b/src/calibre/ebooks/metadata/opf.py
index 021b63ac08..bff9ed5f8a 100644
--- a/src/calibre/ebooks/metadata/opf.py
+++ b/src/calibre/ebooks/metadata/opf.py
@@ -511,6 +511,8 @@ class OPFCreator(MetaInformation):
                 path = path[len(self.base_path)+1:]
                 manifest.append((path, mt))
             self.manifest = manifest
+        if not self.authors:
+            self.authors = [_('Unknown')]
     
     def create_manifest(self, entries):
         '''
diff --git a/src/calibre/library/database.py b/src/calibre/library/database.py
index dc4f4e31de..9d54afc88c 100644
--- a/src/calibre/library/database.py
+++ b/src/calibre/library/database.py
@@ -1427,6 +1427,8 @@ ALTER TABLE books ADD COLUMN isbn TEXT DEFAULT "" COLLATE NOCASE;
                     open(cpath, 'wb').write(cover)
                     mi.cover = cname
                 f = open(os.path.join(base, sanitize_file_name(name)+'.opf'), 'wb')
+                if not mi.authors:
+                    mi.authors = [_('Unknown')]
                 mi.render(f)
                 f.close()