diff -r e5149789e4ea Lib/asyncio/base_events.py
--- a/Lib/asyncio/base_events.py	Sun Apr 17 20:31:51 2016 +0300
+++ b/Lib/asyncio/base_events.py	Mon Apr 18 11:38:45 2016 -0400
@@ -544,7 +544,10 @@
         if executor is None:
             executor = self._default_executor
             if executor is None:
-                executor = concurrent.futures.ThreadPoolExecutor(_MAX_WORKERS)
+                if compat.PY35:
+                    executor = concurrent.futures.ThreadPoolExecutor()
+                else:
+                    executor = concurrent.futures.ThreadPoolExecutor(_MAX_WORKERS)
                 self._default_executor = executor
         return futures.wrap_future(executor.submit(func, *args), loop=self)