diff --git a/subiquity/server/controllers/timezone.py b/subiquity/server/controllers/timezone.py
index b100fd64..27665ddd 100644
--- a/subiquity/server/controllers/timezone.py
+++ b/subiquity/server/controllers/timezone.py
@@ -78,16 +78,22 @@ class TimeZoneController(SubiquityController):
 
     endpoint = API.timezone
 
-    possible = generate_possible_tzs()
-
     autoinstall_key = model_name = 'timezone'
     autoinstall_schema = {
         'type': 'string',
-        'enum': possible
         }
 
     autoinstall_default = ''
 
+    def __init__(self, *args, **kwargs):
+        self.possible = None
+        super().__init__(*args, **kwargs)
+
+    def get_possible_tzs(self):
+        if self.possible is None:
+            self.possible = generate_possible_tzs()
+        return self.possible
+
     def load_autoinstall_data(self, data):
         self.deserialize(data)
 
@@ -100,7 +106,7 @@ class TimeZoneController(SubiquityController):
     def deserialize(self, data):
         if data is None:
             return
-        if data not in self.possible:
+        if data not in self.get_possible_tzs():
             raise ValueError(f'Unrecognized time zone request "{data}"')
         self.model.set(data)
         if self.model.detect_with_geoip and self.app.geoip.timezone:
diff --git a/subiquity/tests/test_timezonecontroller.py b/subiquity/tests/test_timezonecontroller.py
index 5fba2a47..db1fe706 100644
--- a/subiquity/tests/test_timezonecontroller.py
+++ b/subiquity/tests/test_timezonecontroller.py
@@ -99,6 +99,7 @@ class TestTimeZoneController(SubiTestCase):
     def test_set_tz_escape_dryrun(self, tdc_gettz, subprocess_run):
         tdc_gettz.return_value = tz_utc
         self.tzc.app.dry_run = True
+        self.tzc.possible = ['geoip']
         self.tzc.deserialize('geoip')
         self.assertEqual('sleep', subprocess_run.call_args.args[0][0])