diff --git a/Lib/asyncio/proactor_events.py b/Lib/asyncio/proactor_events.py
index 9b9e0aa7c7f..da204c69d45 100644
--- a/Lib/asyncio/proactor_events.py
+++ b/Lib/asyncio/proactor_events.py
@@ -111,7 +111,7 @@ def _fatal_error(self, exc, message='Fatal error on pipe transport'):
             self._force_close(exc)
 
     def _force_close(self, exc):
-        if self._empty_waiter is not None:
+        if self._empty_waiter is not None and not self._empty_waiter.done():
             if exc is None:
                 self._empty_waiter.set_result(None)
             else:
diff --git a/Misc/NEWS.d/next/Library/2019-01-08-01-54-02.bpo-35682.KDM9lk.rst b/Misc/NEWS.d/next/Library/2019-01-08-01-54-02.bpo-35682.KDM9lk.rst
new file mode 100644
index 00000000000..8152bd707ba
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-01-08-01-54-02.bpo-35682.KDM9lk.rst
@@ -0,0 +1,2 @@
+Fix ``asyncio.ProactorEventLoop.sendfile()``: don't attempt to set the result
+of an internal future if it's already done.