diff --git a/README.rst b/README.rst
index 4a46f9267c..8bd8dd13e6 100644
--- a/README.rst
+++ b/README.rst
@@ -65,11 +65,10 @@ Building the documentation
 To build the Cretonne documentation, you need the `Sphinx documentation
 generator <http://www.sphinx-doc.org/>`_::
 
-    $ pip install sphinx==1.3.5 sphinx-autobuild
+    $ pip install sphinx>=1.4 sphinx-autobuild sphinx_rtd_theme
     $ cd cretonne/docs
     $ make html
     $ open _build/html/index.html
 
-The specific Sphinx version is currently used by Read the Docs. Sphinx 1.4 has
-been released, but produces lots of warnings about four-column indices. We'll
-upgrade when Read the Docs does.
+We don't support Sphinx versions before 1.4 since the format of index tuples
+has changed.
diff --git a/cranelift/docs/cton_domain.py b/cranelift/docs/cton_domain.py
index 2f56b5625e..23204f02e7 100644
--- a/cranelift/docs/cton_domain.py
+++ b/cranelift/docs/cton_domain.py
@@ -65,7 +65,8 @@ class CtonObject(ObjectDescription):
         indextext = self.get_index_text(name)
         if indextext:
             self.indexnode['entries'].append(('single', indextext,
-                                              targetname, ''))
+                                              targetname, '', None))
+
 
 # Type variables are indicated as %T.
 typevar = re.compile('(\%[A-Z])')
@@ -113,6 +114,7 @@ class CtonType(CtonObject):
     def get_index_text(self, name):
         return name + ' (IL type)'
 
+
 sep_equal = re.compile('\s*=\s*')
 sep_comma = re.compile('\s*,\s*')