diff --git a/Lib/asyncio/proactor_events.py b/Lib/asyncio/proactor_events.py
index 9b8ae064a8926b..756ef184565f2e 100644
--- a/Lib/asyncio/proactor_events.py
+++ b/Lib/asyncio/proactor_events.py
@@ -12,6 +12,7 @@
 import warnings
 import signal
 import collections
+import threading
 
 from . import base_events
 from . import constants
@@ -627,7 +628,8 @@ def __init__(self, proactor):
         proactor.set_loop(self)
         self._make_self_pipe()
         self_no = self._csock.fileno()
-        signal.set_wakeup_fd(self_no)
+        if threading.current_thread() is threading.main_thread():
+            signal.set_wakeup_fd(self_no)
 
     def _make_socket_transport(self, sock, protocol, waiter=None,
                                extra=None, server=None):