diff -ru Python-3.6.1-old/Lib/inspect.py Python-3.6.1-new/Lib/inspect.py
--- Python-3.6.1-old/Lib/inspect.py	2017-03-21 07:32:38.000000000 +0100
+++ Python-3.6.1-new/Lib/inspect.py	2017-04-14 13:35:34.452589707 +0200
@@ -166,7 +166,7 @@
         __globals__     global namespace in which this function was defined
         __annotations__ dict of parameter annotations
         __kwdefaults__  dict of keyword only parameters with defaults"""
-    return isinstance(object, types.FunctionType)
+    return "__code__" in dir(object)
 
 def isgeneratorfunction(object):
     """Return true if the object is a user-defined generator function.