diff --git a/src/trio/_core/_parking_lot.py b/src/trio/_core/_parking_lot.py
index 9fea4e5b2..9dd3b42dd 100644
--- a/src/trio/_core/_parking_lot.py
+++ b/src/trio/_core/_parking_lot.py
@@ -269,11 +269,13 @@ def repark_all(self, new_lot: ParkingLot) -> None:
         """
         return self.repark(new_lot, count=len(self))
 
-    def break_lot(self, task: Task | None) -> None:
+    def break_lot(self, task: Task | None = None) -> None:
         """Break this lot, causing all parked tasks to raise an error, and any
         future tasks attempting to park (and unpark? repark?) to error. The error
         contains a reference to the task sent as a parameter.
         """
+        if task is None:
+            task = _core.current_task()
         self.broken_by = task
 
         for parked_task in self._parked:
diff --git a/src/trio/_core/_tests/test_parking_lot.py b/src/trio/_core/_tests/test_parking_lot.py
index 740b0412c..5bfd00912 100644
--- a/src/trio/_core/_tests/test_parking_lot.py
+++ b/src/trio/_core/_tests/test_parking_lot.py
@@ -240,6 +240,9 @@ async def test_parking_lot_breaker_basic() -> None:
     ):
         trio.lowlevel.remove_parking_lot_breaker(task, lot)
 
+    lot.break_lot()
+    assert lot.broken_by == task
+
 
 async def test_parking_lot_breaker() -> None:
     async def bad_parker(lot: ParkingLot, scope: _core.CancelScope) -> None: