diff --git a/subiquity/models/tests/test_subiquity.py b/subiquity/models/tests/test_subiquity.py
index 042ae3dd..b2ded689 100644
--- a/subiquity/models/tests/test_subiquity.py
+++ b/subiquity/models/tests/test_subiquity.py
@@ -13,6 +13,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import datetime
 import fnmatch
 import json
 import re
@@ -264,11 +265,13 @@ class TestSubiquityModel(unittest.IsolatedAsyncioTestCase):
             self.assertEqual(expected_error, str(ctx.exception))
 
     @mock.patch("subiquity.models.subiquity.lsb_release")
-    @mock.patch("subiquitycore.file_util.datetime.datetime")
+    @mock.patch("subiquitycore.file_util.datetime.datetime", wraps=datetime.datetime)
     def test_cloud_init_files_emits_datasource_config_and_clean_script(
-        self, datetime, lsb_release
+        self, m_datetime, lsb_release
     ):
-        datetime.utcnow.return_value = "2004-03-05 ..."
+        m_datetime.now.return_value = datetime.datetime(
+            2004, 3, 5, tzinfo=datetime.timezone.utc
+        )
         main_user = IdentityData(
             username="mainuser", crypted_password="sample_pass", hostname="somehost"
         )
@@ -296,7 +299,7 @@ grub_dpkg:
             # NETPLAN_CONFIG_ROOT_READ_ONLY is True
             "/etc/cloud/cloud.cfg.d/90-installer-network.cfg"
         )
-        header = "# Autogenerated by Subiquity: 2004-03-05 ... UTC\n"
+        header = "# Autogenerated by Subiquity: 2004-03-05 00:00:00 UTC\n"
         with self.subTest(
             "Stable releases Jammy do not disable cloud-init."
             " NETPLAN_ROOT_READ_ONLY=True uses cloud-init networking"
diff --git a/subiquity/server/ubuntu_advantage.py b/subiquity/server/ubuntu_advantage.py
index 48abc8fd..640d4637 100644
--- a/subiquity/server/ubuntu_advantage.py
+++ b/subiquity/server/ubuntu_advantage.py
@@ -17,6 +17,7 @@ helper. """
 
 import asyncio
 import contextlib
+import datetime
 import json
 import logging
 import os
@@ -328,10 +329,10 @@ class UAInterface:
         info = await self.get_subscription_status(token)
 
         # Sometimes, a time zone offset of 0 is replaced by the letter Z. This
-        # is specified in RFC 3339 but not supported by fromisoformat.
-        # See https://bugs.python.org/issue35829
+        # is specified in RFC 3339 but not supported by fromisoformat before
+        # Python 3.11. See https://bugs.python.org/issue35829
         expiration = dt.fromisoformat(info["expires"].replace("Z", "+00:00"))
-        if expiration.timestamp() <= dt.utcnow().timestamp():
+        if expiration <= dt.now(datetime.timezone.utc):
             raise ExpiredTokenError(token, expires=info["expires"])
 
         def is_activable_service(service: dict) -> bool:
diff --git a/subiquitycore/file_util.py b/subiquitycore/file_util.py
index c1e48e50..f31509d1 100644
--- a/subiquitycore/file_util.py
+++ b/subiquitycore/file_util.py
@@ -70,7 +70,7 @@ def write_file(filename, content, **kwargs):
 
 
 def generate_timestamped_header() -> str:
-    now = datetime.datetime.utcnow()
+    now = datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None)
     return f"# Autogenerated by Subiquity: {now} UTC\n"