diff --git a/src/risotto/machine.py b/src/risotto/machine.py
index f463cb1..84fa5e7 100644
--- a/src/risotto/machine.py
+++ b/src/risotto/machine.py
@@ -332,10 +332,9 @@ class Loader:
 """)
 
     def add_tls(self):
-        zones = set()
         dns_module_name = None
         for host in self.servers_json['hosts'].values():
-            zones = [self.servers_json['zones']['external_zone'], None]
+            zones = [self.servers_json['zones']['external_zone']]
             for server_name, datas in host['servers'].items():
                 if not 'applicationservice' in datas:
                     raise Exception(f'cannot find applicationservice for "{server_name}"')
@@ -346,13 +345,10 @@ class Loader:
                     if dns_module_name:
                         break
                     zones[1] = datas['provider_zone']
-            if None in zones:
-                zones = []
-            else:
-                if zones[0] == zones[1]:
-                    zones = [zones[0]]
+            if zones[0] == zones[1]:
+                zones = [zones[0]]
             host['servers']['tls'] = {'applicationservice': 'tls',
-                                      'zones_name': list(zones),
+                                      'zones_name': zones,
                                       }
 
     def load_dictionaries(self, cfg, module_info, server_name, rougail):