diff --git a/src/doc/rustc-dev-guide/.gitignore b/src/doc/rustc-dev-guide/.gitignore
index 7585238efedf..b8cb34883f58 100644
--- a/src/doc/rustc-dev-guide/.gitignore
+++ b/src/doc/rustc-dev-guide/.gitignore
@@ -1 +1,4 @@
 book
+
+# prevent accidentally changes
+book.toml