diff --git a/book.toml b/book.toml
index 60770d4eee..45ae5fd944 100644
--- a/book.toml
+++ b/book.toml
@@ -6,3 +6,6 @@ author = "The Rust Community"
 [output.html.playpen]
 editable = true
 editor = "ace"
+
+[output.html.fold]
+enable = true