diff --git a/flask_babel/__init__.py b/flask_babel/__init__.py
index 9f94d22..e2301a1 100644
--- a/flask_babel/__init__.py
+++ b/flask_babel/__init__.py
@@ -10,7 +10,7 @@
 import os
 from dataclasses import dataclass
 from types import SimpleNamespace
-from datetime import datetime
+from datetime import datetime, timezone as stdlib_timezone
 from contextlib import contextmanager
 from typing import List, Callable, Optional, Union
 
@@ -453,7 +453,16 @@ def format_timedelta(datetime_or_timedelta, granularity: str = 'second',
     named `timedeltaformat`.
     """
     if isinstance(datetime_or_timedelta, datetime):
-        datetime_or_timedelta = datetime.utcnow() - datetime_or_timedelta
+        is_aware = (
+            datetime_or_timedelta.tzinfo is not None
+            and datetime_or_timedelta.tzinfo.utcoffset(datetime_or_timedelta)
+            is not None
+        )
+        if is_aware:
+            now = datetime.now(stdlib_timezone.utc)
+        else:
+            now = datetime.utcnow()
+        datetime_or_timedelta = now - datetime_or_timedelta
     return dates.format_timedelta(
         datetime_or_timedelta,
         granularity,
diff --git a/tests/test_date_formatting.py b/tests/test_date_formatting.py
index 545a59d..cb81d3c 100644
--- a/tests/test_date_formatting.py
+++ b/tests/test_date_formatting.py
@@ -1,30 +1,57 @@
-from datetime import datetime, timedelta
+import pytz
+from datetime import datetime, timedelta, timezone
 
 import flask
 
 import flask_babel as babel
 from flask_babel import get_babel
+import time_machine
 
 
 def test_basics():
+    london = pytz.timezone("Europe/London")
     app = flask.Flask(__name__)
     babel.Babel(app)
     d = datetime(2010, 4, 12, 13, 46)
+    d_tzinfo_non_dst = london.localize(datetime(2010, 1, 16, 23, 23)) # non-DST
+    d_tzinfo_dst = london.localize(datetime(2010, 8, 12, 5, 13)) # DST
     delta = timedelta(days=6)
 
     with app.test_request_context():
         assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00\u202fPM'
+        assert babel.format_datetime(d_tzinfo_non_dst) == \
+            "Jan 16, 2010, 11:23:00\u202fPM"
+        assert babel.format_datetime(d_tzinfo_dst) == \
+            "Aug 12, 2010, 4:13:00\u202fAM"
         assert babel.format_date(d) == 'Apr 12, 2010'
         assert babel.format_time(d) == '1:46:00\u202fPM'
         assert babel.format_timedelta(delta) == '1 week'
         assert babel.format_timedelta(delta, threshold=1) == '6 days'
 
+        with time_machine.travel(datetime(2010, 4, 12, 14, tzinfo=timezone.utc)):
+            assert babel.format_timedelta(d) == "14 minutes"
+        with time_machine.travel(datetime(2010, 1, 16, 23, 30, tzinfo=timezone.utc)):
+            assert babel.format_timedelta(d_tzinfo_non_dst) == "7 minutes"
+        with time_machine.travel(datetime(2010, 8, 12, 4, 30, tzinfo=timezone.utc)):
+            assert babel.format_timedelta(d_tzinfo_dst) == "17 minutes"
+
     with app.test_request_context():
         get_babel(app).default_timezone = 'Europe/Vienna'
         assert babel.format_datetime(d) == 'Apr 12, 2010, 3:46:00\u202fPM'
+        assert babel.format_datetime(d_tzinfo_non_dst) == \
+            "Jan 17, 2010, 12:23:00\u202fAM"
+        assert babel.format_datetime(d_tzinfo_dst) == \
+            "Aug 12, 2010, 6:13:00\u202fAM"
         assert babel.format_date(d) == 'Apr 12, 2010'
         assert babel.format_time(d) == '3:46:00\u202fPM'
 
+        with time_machine.travel(datetime(2010, 4, 12, 14, tzinfo=timezone.utc)):
+            assert babel.format_timedelta(d) == "14 minutes"
+        with time_machine.travel(datetime(2010, 1, 16, 23, 30, tzinfo=timezone.utc)):
+            assert babel.format_timedelta(d_tzinfo_non_dst) == "7 minutes"
+        with time_machine.travel(datetime(2010, 8, 12, 4, 30, tzinfo=timezone.utc)):
+            assert babel.format_timedelta(d_tzinfo_dst) == "17 minutes"
+
     with app.test_request_context():
         get_babel(app).default_locale = 'de_DE'
         assert babel.format_datetime(d, 'long') == \