diff --git a/roles/jupyterhub/templates/jupyterhub_config.py b/roles/jupyterhub/templates/jupyterhub_config.py
index ee9a6a3f6..5a9819fc7 100644
--- a/roles/jupyterhub/templates/jupyterhub_config.py
+++ b/roles/jupyterhub/templates/jupyterhub_config.py
@@ -1057,7 +1057,7 @@ c.JupyterHub.spawner_class = 'systemdspawner.SystemdSpawner'
 #  
 #  Defaults to an empty set, in which case no user has admin access.
 #  Default: set()
-c.Authenticator.admin_users = set('Admin')
+c.Authenticator.admin_users = set(['Admin'])
 
 ## Set of usernames that are allowed to log in.
 #