diff --git a/zerver/migrations/0262_mutedtopic_date_muted.py b/zerver/migrations/0262_mutedtopic_date_muted.py
index b3014ddcc7..22ee32a792 100644
--- a/zerver/migrations/0262_mutedtopic_date_muted.py
+++ b/zerver/migrations/0262_mutedtopic_date_muted.py
@@ -14,6 +14,6 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='mutedtopic',
             name='date_muted',
-            field=models.DateTimeField(default=datetime.datetime(2020, 1, 1, 0, 0)),
+            field=models.DateTimeField(default=datetime.datetime(2020, 1, 1, 0, 0, tzinfo=datetime.timezone.utc)),
         ),
     ]
diff --git a/zerver/models.py b/zerver/models.py
index 9a308c90fb..468f143c20 100644
--- a/zerver/models.py
+++ b/zerver/models.py
@@ -1491,7 +1491,7 @@ class MutedTopic(models.Model):
     # The default value for date_muted is a few weeks before tracking
     # of when topics were muted was first introduced.  It's designed
     # to be obviously incorrect so that users can tell it's backfilled data.
-    date_muted = models.DateTimeField(default=datetime.datetime(2020, 1, 1, 0, 0, 0, 0))
+    date_muted = models.DateTimeField(default=datetime.datetime(2020, 1, 1, 0, 0, tzinfo=datetime.timezone.utc))
 
     class Meta:
         unique_together = ('user_profile', 'stream', 'topic_name')
diff --git a/zerver/tests/test_digest.py b/zerver/tests/test_digest.py
index 5690853239..716201d047 100644
--- a/zerver/tests/test_digest.py
+++ b/zerver/tests/test_digest.py
@@ -257,8 +257,8 @@ class TestDigestEmailMessages(ZulipTestCase):
     @mock.patch('zerver.lib.digest.timezone_now')
     @override_settings(SEND_DIGEST_EMAILS=True)
     def test_new_stream_link(self, mock_django_timezone: mock.MagicMock) -> None:
-        cutoff = datetime.datetime(year=2017, month=11, day=1)
-        mock_django_timezone.return_value = datetime.datetime(year=2017, month=11, day=5)
+        cutoff = datetime.datetime(year=2017, month=11, day=1, tzinfo=datetime.timezone.utc)
+        mock_django_timezone.return_value = datetime.datetime(year=2017, month=11, day=5, tzinfo=datetime.timezone.utc)
         cordelia = self.example_user('cordelia')
         stream_id = create_stream_if_needed(cordelia.realm, 'New stream')[0].id
         new_stream = gather_new_streams(cordelia, cutoff)[1]
diff --git a/zerver/tests/test_muting.py b/zerver/tests/test_muting.py
index f26c0b9ad0..946df021b2 100644
--- a/zerver/tests/test_muting.py
+++ b/zerver/tests/test_muting.py
@@ -1,5 +1,5 @@
 from django.utils.timezone import now as timezone_now
-from datetime import timedelta, datetime
+from datetime import timedelta, datetime, timezone
 from typing import Any, Dict
 from unittest import mock
 
@@ -70,10 +70,10 @@ class MutedTopicsTests(ZulipTestCase):
             {'stream_id': stream.id, 'topic': 'Verona3', 'op': 'add'},
         ]
 
-        mock_date_muted = datetime.timestamp(datetime(2020, 1, 1))
+        mock_date_muted = datetime(2020, 1, 1, tzinfo=timezone.utc).timestamp()
         for data in payloads:
             with mock.patch('zerver.views.muting.timezone_now',
-                            return_value=datetime(2020, 1, 1)):
+                            return_value=datetime(2020, 1, 1, tzinfo=timezone.utc)):
                 result = self.api_patch(user, url, data)
                 self.assert_json_success(result)
 
@@ -100,7 +100,7 @@ class MutedTopicsTests(ZulipTestCase):
             {'stream': stream.name, 'topic': 'vERONA3', 'op': 'remove'},
             {'stream_id': stream.id, 'topic': 'vEroNA3', 'op': 'remove'},
         ]
-        mock_date_muted = datetime.timestamp(datetime(2020, 1, 1))
+        mock_date_muted = datetime(2020, 1, 1, tzinfo=timezone.utc).timestamp()
 
         for data in payloads:
             add_topic_mute(
@@ -108,7 +108,7 @@ class MutedTopicsTests(ZulipTestCase):
                 stream_id=stream.id,
                 recipient_id=recipient.id,
                 topic_name='Verona3',
-                date_muted=datetime(2020, 1, 1),
+                date_muted=datetime(2020, 1, 1, tzinfo=timezone.utc),
             )
             self.assertIn([stream.name, 'Verona3', mock_date_muted], get_topic_mutes(user))