Index: lib/alexandria/book_providers.rb
===================================================================
--- lib/alexandria/book_providers.rb	(revision 1086)
+++ lib/alexandria/book_providers.rb	(revision 1087)
@@ -46,6 +46,9 @@
         self.instance.notify_observers(:searching, factory.fullname) # new
         results = factory.search(criterion, type)
 
+        # sanity check if at least one valid result is actually found
+        results.delete_if { |book, cover| book.nil? }
+
         if results.length == 0
           self.instance.changed
           self.instance.notify_observers(:not_found, factory.fullname) # new