diff --git a/book.toml b/book.toml
index c2cd24d0b..bf8f63ef2 100644
--- a/book.toml
+++ b/book.toml
@@ -10,6 +10,10 @@ git-repository-url = "https://github.com/rust-lang/reference/"
 edit-url-template = "https://github.com/rust-lang/reference/edit/master/{path}"
 smart-punctuation = true
 
+[output.html.fold]
+enable = true
+level = 0
+
 [output.html.search.chapter]
 "test-summary.md" = { enable = false }
 "grammar.md" = { enable = false }