diff --git a/src/pendulum/datetime.py b/src/pendulum/datetime.py
index 96aff25b..86bd8921 100644
--- a/src/pendulum/datetime.py
+++ b/src/pendulum/datetime.py
@@ -704,7 +704,7 @@ def _subtract_timedelta(self, delta: datetime.timedelta) -> Self:
     # DIFFERENCES
 
     def diff(  # type: ignore[override]
-        self, dt: datetime.datetime | None = None, abs: bool = True
+        self, dt: DateTime | datetime.datetime | None = None, abs: bool = True
     ) -> Interval[datetime.datetime]:
         """
         Returns the difference between two DateTime objects represented as an Interval.