diff --git a/lib/jqueue.py b/lib/jqueue.py
index 743870afede920e0662106ee250b1702c73fb971..78199141c91d437ca62a9dd188851f57358b8c68 100644
--- a/lib/jqueue.py
+++ b/lib/jqueue.py
@@ -80,6 +80,10 @@ class _QueuedOpCode(object):
   @ivar stop_timestamp: timestamp for the end of the execution
 
   """
+  __slots__ = ["input", "status", "result", "log",
+               "start_timestamp", "end_timestamp",
+               "__weakref__"]
+
   def __init__(self, op):
     """Constructor for the _QuededOpCode.
 
@@ -152,6 +156,11 @@ class _QueuedJob(object):
   @ivar change: a Condition variable we use for waiting for job changes
 
   """
+  __slots__ = ["queue", "id", "ops", "run_op_index", "log_serial",
+               "received_timestamp", "start_timestamp", "end_timestamp",
+               "change",
+               "__weakref__"]
+
   def __init__(self, queue, job_id, ops):
     """Constructor for the _QueuedJob.