diff --git a/stdlib/_weakref.pyi b/stdlib/_weakref.pyi
index 2a43de3ff..b6044fac4 100644
--- a/stdlib/_weakref.pyi
+++ b/stdlib/_weakref.pyi
@@ -20,7 +20,7 @@ class ProxyType(Generic[_T]):  # "weakproxy"
 
 class ReferenceType(Generic[_T]):
     __callback__: Callable[[ReferenceType[_T]], Any]
-    def __new__(cls, o: _T, callback: Callable[[ReferenceType[_T]], Any] | None = ...) -> Self: ...
+    def __new__(cls, __o: _T, __callback: Callable[[ReferenceType[_T]], Any] | None = ...) -> Self: ...
     def __call__(self) -> _T | None: ...
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, item: Any) -> GenericAlias: ...