diff --git a/tests/test_time.py b/tests/test_time.py
index 7699770..bd89145 100644
--- a/tests/test_time.py
+++ b/tests/test_time.py
@@ -326,6 +326,18 @@ def test_naturaldate_tz_aware() -> None:
     assert humanize.naturaldate(future.astimezone(pdt)) == "today"
 
 
+def test_naturaldate_accepts_an_explicit_reference_day() -> None:
+    reference = dt.date(2026, 1, 10)
+    assert humanize.naturalday(dt.date(2026, 1, 11), when=reference) == "tomorrow"
+    assert humanize.naturaldate(dt.date(2026, 1, 9), when=reference) == "yesterday"
+    assert humanize.naturaldate(dt.date(2025, 7, 1), when=reference) == "Jul 01 2025"
+
+    plus_fourteen = dt.timezone(dt.timedelta(hours=14))
+    value = dt.datetime(2026, 1, 1, 0, 30, tzinfo=plus_fourteen)
+    instant = dt.datetime(2025, 12, 31, 12, 0, tzinfo=dt.timezone.utc)
+    assert humanize.naturaldate(value, when=instant) == "today"
+
+
 @pytest.mark.parametrize(
     "seconds, expected",
     [