diff --git a/.travis.yml b/.travis.yml
index 8a35d5e..3d7e428 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,6 +17,7 @@ install:
     - pip install setuptools pip --upgrade
     - pip install -e file://$PWD#egg=ipython[test] --upgrade
     - pip install codecov --upgrade
+    - sudo apt-get install graphviz
 script:
     - cd /tmp && iptest --coverage xml && cd -
     # On the latest Python only, make sure that the docs build.
diff --git a/docs/source/conf.py b/docs/source/conf.py
index e060572..20ef8f9 100755
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -57,6 +57,7 @@ extensions = [
     'sphinx.ext.doctest',
     'sphinx.ext.inheritance_diagram',
     'sphinx.ext.intersphinx',
+    'sphinx.ext.graphviz',
     'IPython.sphinxext.ipython_console_highlighting',
     'IPython.sphinxext.ipython_directive',
     'sphinx.ext.napoleon',  # to preprocess docstrings