diff --git a/src/doc/rustc-dev-guide/book.toml b/src/doc/rustc-dev-guide/book.toml
index b5bced996d0b..82a6b59b03f8 100644
--- a/src/doc/rustc-dev-guide/book.toml
+++ b/src/doc/rustc-dev-guide/book.toml
@@ -8,7 +8,9 @@ create-missing = false
 
 [output.html]
 
-[output.html.search]
+[output.html.fold]
+enable = true
+level = 1
 
 [output.linkcheck]
 follow-web-links = true