diff --git a/trio/_core/_parking_lot.py b/trio/_core/_parking_lot.py
index 8b114b5230..e0f57ff8fa 100644
--- a/trio/_core/_parking_lot.py
+++ b/trio/_core/_parking_lot.py
@@ -80,12 +80,12 @@
 _counter = count()
 
 
-@attr.s(frozen=True)
+@attr.s(frozen=True, slots=True)
 class _ParkingLotStatistics:
     tasks_waiting = attr.ib()
 
 
-@attr.s(eq=False, hash=False)
+@attr.s(eq=False, hash=False, slots=True)
 class ParkingLot(metaclass=Final):
     """A fair wait queue with cancellation and requeueing.