diff --git a/.travis.yml b/.travis.yml
index fda4f5cf..c299e6b4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,12 +2,15 @@
 #   http://lint.travis-ci.org/
 language: python
 sudo: false
-python:
-  - 3.6
-  - 2.7
 env:
   - SPHINX_SPEC="Sphinx==1.2.3"
   - SPHINX_SPEC="Sphinx"
+matrix:
+  include:
+    - python: 3.6
+    - python: 2.7
+      env:
+        - SPHINXOPTS='-W'
 cache:
   directories:
     - $HOME/.cache/pip
@@ -23,5 +26,5 @@ script:
   - nosetests numpydoc
   - |
     cd ../doc
-    make html
-    make latexpdf
+    make SPHINXOPTS=$SPHINXOPTS html
+    make SPHINXOPTS=$SPHINXOPTS latexpdf
diff --git a/doc/conf.py b/doc/conf.py
index 5a311bca..ef2788e2 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -41,13 +41,19 @@
     'sphinx.ext.autosummary',
     'sphinx.ext.doctest',
     'sphinx.ext.intersphinx',
-    'sphinx.ext.pngmath',
     'sphinx.ext.todo',
     'numpydoc',
     'sphinx.ext.ifconfig',
     'sphinx.ext.viewcode',
 ]
 
+try:
+    import sphinx.ext.imgmath  # noqa
+except ImportError:
+    extensions.append('sphinx.ext.pngmath')
+else:
+    extensions.append('sphinx.ext.imgmath')
+
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
 
@@ -149,13 +155,12 @@
     html_sidebars = {}
 
 html_title = "%s v%s Manual" % (project, version)
-html_static_path = ['_static']
 html_last_updated_fmt = '%b %d, %Y'
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = []  # ['_static']
 
 # Add any extra paths that contain custom files (such as robots.txt or
 # .htaccess) here, relative to this directory. These files are copied
@@ -264,5 +269,5 @@
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
     'python': ('http://docs.python.org/', None),
-    'scikit-learn': ('http://scikit-learn.org/stable/', None),
+    'scikitlearn': ('http://scikit-learn.org/stable/', None),
 }
diff --git a/doc/format.rst b/doc/format.rst
index 9b3b0ca5..c30ca4fd 100644
--- a/doc/format.rst
+++ b/doc/format.rst
@@ -374,7 +374,7 @@ The sections of a function's docstring are:
          and neural-network techniques," Computers & Geosciences, vol. 22,
          pp. 585-588, 1996.
 
-    which renders as
+    which renders as [1]_:
 
     .. [1] O. McNoleg, "The integration of GIS, remote sensing,
        expert systems and adaptive co-kriging for environmental habitat