diff --git a/travis/build-helper.sh b/travis/build-helper.sh
index d3e0729..5a1908a 100755
--- a/travis/build-helper.sh
+++ b/travis/build-helper.sh
@@ -40,7 +40,7 @@ run() {
 
   Documentation)
     # Generate documentation
-    pip install sphinx
+    pip install sphinx sphinx_bootstrap_theme
     cd doc
     make html
     touch build/html/.nojekyll