diff --git a/lib/constants.py b/lib/constants.py
index 3949f56b7634841e0cd498a7c1dffad91c86510b..05226c03fe0686f88ab84b8f6b4ad7ccf29d9378 100644
--- a/lib/constants.py
+++ b/lib/constants.py
@@ -453,13 +453,19 @@ JOB_STATUS_CANCELED = "canceled"
 JOB_STATUS_SUCCESS = "success"
 JOB_STATUS_ERROR = "error"
 
+# OpCode status
+# not yet finalized
 OP_STATUS_QUEUED = "queued"
 OP_STATUS_WAITLOCK = "waiting"
 OP_STATUS_CANCELING = "canceling"
 OP_STATUS_RUNNING = "running"
+# finalized
 OP_STATUS_CANCELED = "canceled"
 OP_STATUS_SUCCESS = "success"
 OP_STATUS_ERROR = "error"
+OPS_FINALIZED = frozenset([OP_STATUS_CANCELED,
+                           OP_STATUS_SUCCESS,
+                           OP_STATUS_ERROR])
 
 # Execution log types
 ELOG_MESSAGE = "message"
diff --git a/lib/jqueue.py b/lib/jqueue.py
index 083031c077011a5ab339c3699932225ad307d216..20fa1c7b9546cd9252d30222824b1718b1f814d8 100644
--- a/lib/jqueue.py
+++ b/lib/jqueue.py
@@ -313,6 +313,26 @@ class _QueuedJob(object):
 
     return entries
 
+  def MarkUnfinishedOps(self, status, result):
+    """Mark unfinished opcodes with a given status and result.
+
+    This is an utility function for marking all running or waiting to
+    be run opcodes with a given status. Opcodes which are already
+    finalised are not changed.
+
+    @param status: a given opcode status
+    @param result: the opcode result
+
+    """
+    not_marked = True
+    for op in self.ops:
+      if op.status in constants.OPS_FINALIZED:
+        assert not_marked, "Finalized opcodes found after non-finalized ones"
+        continue
+      op.status = status
+      op.result = result
+      not_marked = False
+
 
 class _JobQueueWorker(workerpool.BaseWorker):
   """The actual job workers.
@@ -593,9 +613,8 @@ class JobQueue(object):
                           constants.JOB_STATUS_CANCELING):
             logging.warning("Unfinished job %s found: %s", job.id, job)
             try:
-              for op in job.ops:
-                op.status = constants.OP_STATUS_ERROR
-                op.result = "Unclean master daemon shutdown"
+              job.MarkUnfinishedOps(constants.OP_STATUS_ERROR,
+                                    "Unclean master daemon shutdown")
             finally:
               self.UpdateJobUnlocked(job)
 
@@ -1157,8 +1176,7 @@ class JobQueue(object):
     elif job_status == constants.JOB_STATUS_WAITLOCK:
       # The worker will notice the new status and cancel the job
       try:
-        for op in job.ops:
-          op.status = constants.OP_STATUS_CANCELING
+        job.MarkUnfinishedOps(constants.OP_STATUS_CANCELING, None)
       finally:
         self.UpdateJobUnlocked(job)
       return (True, "Job %s will be canceled" % job.id)
@@ -1169,9 +1187,8 @@ class JobQueue(object):
 
     """
     try:
-      for op in job.ops:
-        op.status = constants.OP_STATUS_CANCELED
-        op.result = "Job canceled by request"
+      job.MarkUnfinishedOps(constants.OP_STATUS_CANCELED,
+                            "Job canceled by request")
     finally:
       self.UpdateJobUnlocked(job)