diff --git a/ccserver/jobs.py b/ccserver/jobs.py
index bc37ba45d1f3d9ca42828e8d3bf9d442e30c558d..14052eb9728112b64cc956716079f2876372d2d3 100644
--- a/ccserver/jobs.py
+++ b/ccserver/jobs.py
@@ -151,6 +151,10 @@ class BaseJob(dict, Thread, object):
             the job.
         '''
 
+        if self['done']:
+            raise JobError('Job is done')
+        if self['cancelled']:
+            raise JobError('Job is already cancelled')
         self['cancelled'] = True
         self.report('cancelling')