diff --git a/master.cfg b/master.cfg
index 88e3bfa..74f865c 100644
--- a/master.cfg
+++ b/master.cfg
@@ -829,7 +829,7 @@ def load_config (c):
 
     c['slaves'] = [BuildSlave (slave['name'], passwd[slave['name']],
                                max_builds = 1,
-                               notify_on_missing = slave['admin'],
+                               notify_on_missing = [ str (slave['admin']) ],
                                missing_timeout = 300,
                                properties = { 'jobs' : slave['jobs'],
                                               'randomWait' : "%d" % random.randrange (1, 30) })