diff --git a/index.rmd b/index.rmd
index 5fa6f6a..887d89f 100644
--- a/index.rmd
+++ b/index.rmd
@@ -8,6 +8,7 @@ github-repo: hadley/r4ds
 twitter-handle: hadley
 cover-image: cover.png
 site: bookdown::bookdown_site
+documentclass: book
 ---
 
 # Welcome {-}