diff --git a/src/humanize/time.py b/src/humanize/time.py
index 1c65d8e6..25172ebe 100644
--- a/src/humanize/time.py
+++ b/src/humanize/time.py
@@ -12,6 +12,7 @@
 import typing
 from enum import Enum
 from functools import total_ordering
+from typing import Any
 
 from .i18n import _gettext as _
 from .i18n import _ngettext
@@ -245,10 +246,10 @@ def naturaltime(
     Returns:
         str: A natural representation of the input in a resolution that makes sense.
     """
-    now = when or _now()
+    value = _convert_aware_datetime(value)
+    when = _convert_aware_datetime(when)
 
-    if isinstance(value, dt.datetime) and value.tzinfo is not None:
-        value = dt.datetime.fromtimestamp(value.timestamp())
+    now = when or _now()
 
     date, delta = _date_and_delta(value, now=now)
     if date is None:
@@ -266,6 +267,15 @@ def naturaltime(
     return str(ago % delta)
 
 
+def _convert_aware_datetime(
+    value: dt.datetime | dt.timedelta | float | None,
+) -> Any:
+    """Convert aware datetime to naive datetime and pass through any other type."""
+    if isinstance(value, dt.datetime) and value.tzinfo is not None:
+        value = dt.datetime.fromtimestamp(value.timestamp())
+    return value
+
+
 def naturalday(value: dt.date | dt.datetime, format: str = "%b %d") -> str:
     """Return a natural day.
 
diff --git a/tests/test_time.py b/tests/test_time.py
index a4d40f90..0396be26 100644
--- a/tests/test_time.py
+++ b/tests/test_time.py
@@ -444,6 +444,40 @@ def test_naturaltime_timezone(test_input: dt.datetime, expected: str) -> None:
     assert humanize.naturaltime(test_input) == expected
 
 
+@freeze_time("2020-02-02")
+@pytest.mark.parametrize(
+    "test_input, expected",
+    [
+        (NOW_UTC, "now"),
+        (NOW_UTC - dt.timedelta(seconds=1), "a second ago"),
+        (NOW_UTC - dt.timedelta(seconds=30), "30 seconds ago"),
+        (NOW_UTC - dt.timedelta(minutes=1, seconds=30), "a minute ago"),
+        (NOW_UTC - dt.timedelta(minutes=2), "2 minutes ago"),
+        (NOW_UTC - dt.timedelta(hours=1, minutes=30, seconds=30), "an hour ago"),
+        (NOW_UTC - dt.timedelta(hours=23, minutes=50, seconds=50), "23 hours ago"),
+        (NOW_UTC - dt.timedelta(days=1), "a day ago"),
+        (NOW_UTC - dt.timedelta(days=500), "1 year, 4 months ago"),
+        (NOW_UTC - dt.timedelta(days=365 * 2 + 35), "2 years ago"),
+        (NOW_UTC + dt.timedelta(seconds=1), "a second from now"),
+        (NOW_UTC + dt.timedelta(seconds=30), "30 seconds from now"),
+        (NOW_UTC + dt.timedelta(minutes=1, seconds=30), "a minute from now"),
+        (NOW_UTC + dt.timedelta(minutes=2), "2 minutes from now"),
+        (NOW_UTC + dt.timedelta(hours=1, minutes=30, seconds=30), "an hour from now"),
+        (NOW_UTC + dt.timedelta(hours=23, minutes=50, seconds=50), "23 hours from now"),
+        (NOW_UTC + dt.timedelta(days=1), "a day from now"),
+        (NOW_UTC + dt.timedelta(days=500), "1 year, 4 months from now"),
+        (NOW_UTC + dt.timedelta(days=365 * 2 + 35), "2 years from now"),
+        # regression tests for bugs in post-release humanize
+        (NOW_UTC + dt.timedelta(days=10000), "27 years from now"),
+        (NOW_UTC - dt.timedelta(days=365 + 35), "1 year, 1 month ago"),
+        (NOW_UTC - dt.timedelta(days=365 * 2 + 65), "2 years ago"),
+        (NOW_UTC - dt.timedelta(days=365 + 4), "1 year, 4 days ago"),
+    ],
+)
+def test_naturaltime_timezone_when(test_input: dt.datetime, expected: str) -> None:
+    assert humanize.naturaltime(test_input, when=NOW_UTC) == expected
+
+
 @pytest.mark.parametrize(
     "val, min_unit, expected",
     [