diff --git a/stdlib/types.pyi b/stdlib/types.pyi
index 65262ece0..c0f274538 100644
--- a/stdlib/types.pyi
+++ b/stdlib/types.pyi
@@ -218,6 +218,8 @@ class AsyncGeneratorType(AsyncGenerator[_T_co, _T_contra]):
     @overload
     def athrow(self, __typ: BaseException, __val: None = ..., __tb: TracebackType | None = ...) -> Awaitable[_T_co]: ...
     def aclose(self) -> Awaitable[None]: ...
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, __item: Any) -> GenericAlias: ...
 
 @final
 class CoroutineType(Coroutine[_T_co, _T_contra, _V_co]):