Update to 2021 edition
diff --git a/book.toml b/book.toml
index a2011c6..693aca4 100644
--- a/book.toml
+++ b/book.toml
@@ -32,4 +32,4 @@
"./arc.html" = "./arc-mutex/arc.html"
[rust]
-edition = "2018"
+edition = "2021"
diff --git a/src/intro.md b/src/intro.md
index 4e77ffa..323c0ce 100644
--- a/src/intro.md
+++ b/src/intro.md
@@ -39,7 +39,7 @@
The Rustonomicon is not a place to exhaustively describe the semantics and guarantees of every single API in the standard library, nor is it a place to exhaustively describe every feature of Rust.
-Unless otherwise noted, Rust code in this book uses the Rust 2018 edition.
+Unless otherwise noted, Rust code in this book uses the Rust 2021 edition.
[trpl]: ../book/index.html
[ref]: ../reference/index.html
