diff --git a/tests/test_time.py b/tests/test_time.py
index d8268c7..a140b52 100644
--- a/tests/test_time.py
+++ b/tests/test_time.py
@@ -96,7 +96,6 @@ def test_naturaldelta_nomonths(test_input: dt.timedelta, expected: str) -> None:
         (23.5, "23 seconds"),
         (30, "30 seconds"),
         (dt.timedelta(microseconds=13), "a moment"),
-        (dt.timedelta(microseconds=-13), "a moment"),
         (dt.timedelta(minutes=1, seconds=30), "a minute"),
         (dt.timedelta(minutes=2), "2 minutes"),
         (dt.timedelta(hours=1, minutes=30, seconds=30), "an hour"),
@@ -131,6 +130,8 @@ def test_naturaldelta_nomonths(test_input: dt.timedelta, expected: str) -> None:
 )
 def test_naturaldelta(test_input: int | dt.timedelta, expected: str) -> None:
     assert humanize.naturaldelta(test_input) == expected
+    if not isinstance(test_input, str):
+        assert humanize.naturaldelta(-test_input) == expected
 
 
 @freeze_time("2020-02-02")