diff --git a/qpid/codec.py b/qpid/codec.py
index 3b61677..c9f12e2 100644
--- a/qpid/codec.py
+++ b/qpid/codec.py
@@ -354,7 +354,7 @@
     encodes an UNSIGNED long long (64 bits) data 'o' in network byte order
     AMQP 0-9-1 type: long-long-uint
     """
-    self.pack("!Q", o)
+    self.pack("!Q", long(o))
 
   def decode_longlong(self):
     """