diff --git a/.travis.yml b/.travis.yml
index ae1523f53c..d6c15faf80 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -105,6 +105,7 @@ matrix:
             - *packages
             - coccinelle
             - gcc-7
+            - python3-sphinx
     # Linux, gcc, Rust (latest stable).
     # This is allowed to fail, update allow_failures if the env changes.
     - os: linux