diff -up tornado-4.2.1/tornado/util.py.argspec tornado-4.2.1/tornado/util.py
--- tornado-4.2.1/tornado/util.py.argspec	2015-10-14 13:07:58.133043900 +0200
+++ tornado-4.2.1/tornado/util.py	2015-10-14 13:09:03.530841229 +0200
@@ -18,6 +18,11 @@ import os
 import sys
 import zlib
 
+try:
+    from inspect import getfullargspec as getargspec
+except:
+    from inspect import getargspec
+
 
 try:
     xrange  # py2
@@ -284,7 +289,7 @@ class ArgReplacer(object):
     def __init__(self, func, name):
         self.name = name
         try:
-            self.arg_pos = inspect.getargspec(func).args.index(self.name)
+            self.arg_pos = getargspec(func).args.index(self.name)
         except ValueError:
             # Not a positional parameter
             self.arg_pos = None