diff -Nur tornado-4.5.1.orig/docs/conf.py tornado-4.5.1/docs/conf.py
--- tornado-4.5.1.orig/docs/conf.py	2017-06-27 17:39:55.881133239 +0000
+++ tornado-4.5.1/docs/conf.py	2017-06-27 17:40:59.910682166 +0000
@@ -16,7 +16,6 @@
     "sphinx.ext.autodoc",
     "sphinx.ext.coverage",
     "sphinx.ext.doctest",
-    "sphinx.ext.intersphinx",
     "sphinx.ext.viewcode",
     ]
 
@@ -81,10 +80,6 @@
     ('index', 'tornado.tex', 'Tornado Documentation', 'The Tornado Authors', 'manual', False),
     ]
 
-intersphinx_mapping = {
-    'python': ('https://docs.python.org/3.5/', None),
-    }
-
 on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
 
 # On RTD we can't import sphinx_rtd_theme, but it will be applied by
