diff --git a/.travis.yml b/.travis.yml
index 5d7d7e38b..1869c12aa 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,7 @@ addons:
       - python-lxml # because pip installation is slow
       - pdftk
       - libreoffice
+      - graphviz
 
 language: python