diff --git a/src/calibre/ebooks/metadata/sources/amazon.py b/src/calibre/ebooks/metadata/sources/amazon.py
index 8483698e28..31d815af63 100644
--- a/src/calibre/ebooks/metadata/sources/amazon.py
+++ b/src/calibre/ebooks/metadata/sources/amazon.py
@@ -338,7 +338,7 @@ class Amazon(Source):
                     q['field-author'] = ' '.join(author_tokens)
 
         if not ('field-keywords' in q or 'field-isbn' in q or
-                ('field-title' in q and 'field-author' in q)):
+                ('field-title' in q)):
             # Insufficient metadata to make an identify query
             return None
 
diff --git a/src/calibre/ebooks/metadata/sources/base.py b/src/calibre/ebooks/metadata/sources/base.py
index e74e4f5042..c20cb1db83 100644
--- a/src/calibre/ebooks/metadata/sources/base.py
+++ b/src/calibre/ebooks/metadata/sources/base.py
@@ -291,10 +291,10 @@ class Source(Plugin):
                     parts = parts[1:] + parts[:1]
                 for tok in parts:
                     tok = remove_pat.sub('', tok).strip()
-                    if len(tok) > 2 and tok.lower() not in ('von', ):
+                    if len(tok) > 2 and tok.lower() not in ('von', 'van',
+                            _('Unknown').lower()):
                         yield tok
 
-
     def get_title_tokens(self, title, strip_joiners=True, strip_subtitle=False):
         '''
         Take a title and return a list of tokens useful for an AND search query.