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 10:28:39 2016 -0400
@@ -43,9 +43,6 @@
 __all__ = ['BaseEventLoop']
 
 
-# Argument for default thread pool executor creation.
-_MAX_WORKERS = 5
-
 # Minimum number of _scheduled timer handles before cleanup of
 # cancelled handles is performed.
 _MIN_SCHEDULED_TIMER_HANDLES = 100
@@ -544,7 +541,7 @@
         if executor is None:
             executor = self._default_executor
             if executor is None:
-                executor = concurrent.futures.ThreadPoolExecutor(_MAX_WORKERS)
+                executor = concurrent.futures.ThreadPoolExecutor()
                 self._default_executor = executor
         return futures.wrap_future(executor.submit(func, *args), loop=self)