diff --git a/nilmdb/utils/serializer.py b/nilmdb/utils/serializer.py
index bf21696..4ffa3c4 100644
--- a/nilmdb/utils/serializer.py
+++ b/nilmdb/utils/serializer.py
@@ -117,7 +117,10 @@ def serializer_proxy(obj_or_type):
             return ret
 
         def __del__(self):
-            self.__call_queue.put((None, None, None, None))
-            self.__thread.join()
+            try:
+                self.__call_queue.put((None, None, None, None))
+                self.__thread.join()
+            except TypeError: # pragma: no cover
+                pass
 
     return SerializerObjectProxy(obj_or_type)