diff --git a/ccserver/jobs.py b/ccserver/jobs.py
index c525bfbd059ecba1993088dd4b5290c5eb97f418..2b7b60e936e868d8d98d439bf91e55aea5b959a7 100644
--- a/ccserver/jobs.py
+++ b/ccserver/jobs.py
@@ -307,6 +307,8 @@ class JobsManager(object):
 
         if job is None:
             raise UnknownJobError('Invalid job id: %r' % jobid)
+        elif job.get('_hidden', False):
+            raise UnknownJobError('Invalid job id: %r (hidden)' % jobid)
         else:
             job.cancel()