diff --git a/bookops_worldcat/authorize.py b/bookops_worldcat/authorize.py
index e83647d..e71a26a 100644
--- a/bookops_worldcat/authorize.py
+++ b/bookops_worldcat/authorize.py
@@ -161,6 +161,7 @@ def _hasten_expiration_time(self, utc_stamp_str: str) -> datetime.datetime:
         utcstamp = datetime.datetime.strptime(
             utc_stamp_str, "%Y-%m-%d %H:%M:%SZ"
         ) - datetime.timedelta(seconds=1)
+        utcstamp = utcstamp.replace(tzinfo=datetime.timezone.utc)
         return utcstamp
 
     def _parse_server_response(self, response: requests.Response) -> None:
diff --git a/tests/conftest.py b/tests/conftest.py
index 8821e95..e78db1e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -28,7 +28,7 @@ def live_keys():
 class FakeUtcNow(datetime.datetime):
     @classmethod
     def now(cls, tzinfo=datetime.timezone.utc):
-        return cls(2020, 1, 1, 17, 0, 0, 0)
+        return cls(2020, 1, 1, 17, 0, 0, 0, tzinfo=datetime.timezone.utc)
 
 
 @pytest.fixture
diff --git a/tests/test_authorize.py b/tests/test_authorize.py
index 7c559e0..4e96d41 100644
--- a/tests/test_authorize.py
+++ b/tests/test_authorize.py
@@ -265,7 +265,9 @@ def test_hasten_expiration_time(self, mock_token):
         token = mock_token
         timestamp = token._hasten_expiration_time(utc_stamp)
         assert isinstance(timestamp, datetime.datetime)
-        assert timestamp == datetime.datetime(2020, 1, 1, 17, 19, 58, 0)
+        assert timestamp == datetime.datetime(
+            2020, 1, 1, 17, 19, 58, 0, tzinfo=datetime.timezone.utc
+        )
 
     def test_payload(self, mock_successful_post_token_response):
         token = WorldcatAccessToken(
diff --git a/tests/test_metadata_api.py b/tests/test_metadata_api.py
index da1a8fe..a6d615d 100644
--- a/tests/test_metadata_api.py
+++ b/tests/test_metadata_api.py
@@ -49,7 +49,7 @@ def test_get_new_access_token(self, mock_token, mock_now):
             assert session.authorization.is_expired() is True
             session._get_new_access_token()
             assert session.authorization.token_expires_at == datetime.datetime(
-                2020, 1, 1, 17, 19, 58
+                2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
             )
             assert session.authorization.is_expired() is False
 
@@ -209,7 +209,7 @@ def test_get_brief_bib_with_stale_token(
         assert stub_session.authorization.is_expired() is True
         response = stub_session.get_brief_bib(oclcNumber=12345)
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 200
@@ -254,7 +254,7 @@ def test_get_full_bib_with_stale_token(self, stub_session, mock_session_response
         response = stub_session.get_full_bib(12345)
         assert stub_session.authorization.is_expired() is False
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert response.status_code == 200
 
@@ -281,7 +281,7 @@ def test_holding_get_status_with_stale_token(
         response = stub_session.holding_get_status(12345)
         assert stub_session.authorization.is_expired() is False
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert response.status_code == 200
 
@@ -305,7 +305,7 @@ def test_holding_set_stale_token(self, stub_session, mock_session_response):
         assert stub_session.authorization.is_expired() is True
         response = stub_session.holding_set(850940548)
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 201
@@ -332,7 +332,7 @@ def test_holding_unset_stale_token(
         assert stub_session.authorization.is_expired() is True
         response = stub_session.holding_unset(850940548)
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 200
@@ -370,7 +370,7 @@ def test_holdings_set_stale_token(
             assert stub_session.authorization.is_expired() is True
             stub_session.holdings_set([850940548, 850940552, 850940554])
             assert stub_session.authorization.token_expires_at == datetime.datetime(
-                2020, 1, 1, 17, 19, 58
+                2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
             )
             assert stub_session.authorization.is_expired() is False
 
@@ -409,7 +409,7 @@ def test_holdings_unset_stale_token(
             assert stub_session.authorization.is_expired() is True
             stub_session.holdings_unset([850940548, 850940552, 850940554])
             assert stub_session.authorization.token_expires_at == datetime.datetime(
-                2020, 1, 1, 17, 19, 58
+                2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
             )
             assert stub_session.authorization.is_expired() is False
 
@@ -447,7 +447,7 @@ def test_holdings_set_multi_institutions_stale_token(
                 oclcNumber=850940548, instSymbols="NYP,BKL"
             )
             assert stub_session.authorization.token_expires_at == datetime.datetime(
-                2020, 1, 1, 17, 19, 58
+                2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
             )
             assert stub_session.authorization.is_expired() is False
 
@@ -501,7 +501,7 @@ def test_holdings_unset_multi_institutions_stale_token(
                 oclcNumber=850940548, instSymbols="NYP,BKL"
             )
             assert stub_session.authorization.token_expires_at == datetime.datetime(
-                2020, 1, 1, 17, 19, 58
+                2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
             )
             assert stub_session.authorization.is_expired() is False
 
@@ -521,7 +521,7 @@ def test_search_brief_bibs_other_editions_stale_token(
         assert stub_session.authorization.is_expired() is True
         response = stub_session.search_brief_bib_other_editions(12345)
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 200
@@ -552,7 +552,7 @@ def test_search_brief_bibs_with_stale_token(
         assert stub_session.authorization.is_expired() is True
         response = stub_session.search_brief_bibs(q="ti:foo")
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 200
@@ -594,7 +594,7 @@ def test_search_current_control_numbers_with_stale_token(
         assert stub_session.authorization.is_expired() is True
         response = stub_session.search_current_control_numbers(["12345", "65891"])
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 207
@@ -625,7 +625,7 @@ def test_search_general_holdings_with_stale_token(
         assert stub_session.authorization.is_expired() is True
         response = stub_session.search_general_holdings(oclcNumber=12345)
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 200
@@ -661,7 +661,7 @@ def test_search_shared_print_holdings_with_stale_token(
         assert stub_session.authorization.is_expired() is True
         response = stub_session.search_shared_print_holdings(oclcNumber=12345)
         assert stub_session.authorization.token_expires_at == datetime.datetime(
-            2020, 1, 1, 17, 19, 58
+            2020, 1, 1, 17, 19, 58, tzinfo=datetime.timezone.utc
         )
         assert stub_session.authorization.is_expired() is False
         assert response.status_code == 200