diff --git a/third_party/2/concurrent/futures/__init__.pyi b/third_party/2/concurrent/futures/__init__.pyi
index bbec6ad67..49c0de6e2 100644
--- a/third_party/2/concurrent/futures/__init__.pyi
+++ b/third_party/2/concurrent/futures/__init__.pyi
@@ -15,7 +15,7 @@ class Future(Generic[_T]):
     def exception(self, timeout: float = ...) -> Any: ...
     def add_done_callback(self, fn: Callable[[Future], Any]) -> None: ...
 
-    def set_running_or_notify_cancel(self) -> None: ...
+    def set_running_or_notify_cancel(self) -> bool: ...
     def set_result(self, result: _T) -> None: ...
     def set_exception(self, exception: Any) -> None: ...