diff --git a/stdlib/3/asyncio/tasks.pyi b/stdlib/3/asyncio/tasks.pyi
index 6a193f428..6fe13f57e 100644
--- a/stdlib/3/asyncio/tasks.pyi
+++ b/stdlib/3/asyncio/tasks.pyi
@@ -24,7 +24,7 @@ ALL_COMPLETED: str
 def as_completed(fs: Sequence[_FutureT[_T]], *, loop: AbstractEventLoop = ...,
                  timeout: Optional[float] = ...) -> Iterator[Future[_T]]: ...
 def ensure_future(coro_or_future: _FutureT[_T],
-                  *, loop: AbstractEventLoop = ...) -> Future[_T]: ...
+                  *, loop: Optional[AbstractEventLoop] = ...) -> Future[_T]: ...
 # Prior to Python 3.7 'async' was an alias for 'ensure_future'.
 # It became a keyword in 3.7.
 @overload