diff --git a/src/calibre/ebooks/metadata/amazon.py b/src/calibre/ebooks/metadata/amazon.py
index 6eb106c862..c617a2beaf 100644
--- a/src/calibre/ebooks/metadata/amazon.py
+++ b/src/calibre/ebooks/metadata/amazon.py
@@ -121,6 +121,19 @@ def report(verbose):
 class AmazonError(Exception):
     pass
 
+class ThreadwithResults(Thread):
+    def __init__(self, func, *args, **kargs):
+        self.func = func
+        self.args = args
+        self.kargs = kargs
+        self.result = None
+        Thread.__init__(self)
+
+    def get_result(self):
+        return self.result
+
+    def run(self):
+        self.result = self.func(*self.args, **self.kargs)
 
 class Query(object):
 
diff --git a/src/calibre/ebooks/metadata/fetch.py b/src/calibre/ebooks/metadata/fetch.py
index a7709f88b4..dbf0db7bfe 100644
--- a/src/calibre/ebooks/metadata/fetch.py
+++ b/src/calibre/ebooks/metadata/fetch.py
@@ -299,8 +299,8 @@ def search(title=None, author=None, publisher=None, isbn=None, isbndb_key=None,
     with MetadataSources(fetchers) as manager:
         manager(title, author, publisher, isbn, verbose)
         manager.join()
-
-    results = list(fetchers[0].results) if fetchers else []
+    
+    results = list(fetchers[0].results) if fetchers[0].results else []
     for fetcher in fetchers[1:]:
         merge_results(results, fetcher.results)
 
diff --git a/src/calibre/ebooks/metadata/isbndb.py b/src/calibre/ebooks/metadata/isbndb.py
index b1a69e37c0..787d70eb51 100644
--- a/src/calibre/ebooks/metadata/isbndb.py
+++ b/src/calibre/ebooks/metadata/isbndb.py
@@ -25,7 +25,7 @@ class ISBNDB(MetadataSource):
 
     def fetch(self):
         if not self.site_customization:
-            return
+            return None
         try:
             self.results = search(self.title, self.book_author, self.publisher, self.isbn,
                                    max_results=10, verbose=self.verbose, key=self.site_customization)
@@ -231,6 +231,7 @@ def search(title=None, author=None, publisher=None, isbn=None,
     #List of entry
     ans = ResultList()
     ans.populate(entries, verbose)
+    ans = [x for x in ans if x is not None]
     return list(dict((book.isbn, book) for book in ans).values())
 
 def option_parser():