diff --git a/.travis.yml b/.travis.yml
index 61c1efa0..dab7dee3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -26,6 +26,7 @@ addons:
     - g++-multilib
     # These are needed for building and deploying the docs.
     - python3-markdown
+    - python3-pygments
     - python3-setuptools
     - ruby-sass