diff --git a/src/tools/tidy/Cargo.toml b/src/tools/tidy/Cargo.toml
index 4835c2202104..d995106ae025 100644
--- a/src/tools/tidy/Cargo.toml
+++ b/src/tools/tidy/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "tidy"
 version = "0.1.0"
-edition = "2021"
+edition = "2024"
 autobins = false
 
 [dependencies]
diff --git a/src/tools/tidy/src/main.rs b/src/tools/tidy/src/main.rs
index 1eb5485f2b86..a67f7a511b59 100644
--- a/src/tools/tidy/src/main.rs
+++ b/src/tools/tidy/src/main.rs
@@ -15,11 +15,12 @@ use std::{env, process};
 use tidy::*;
 
 fn main() {
-    // Running Cargo will read the libstd Cargo.toml
+    // Enable nightly, because Cargo will read the libstd Cargo.toml
     // which uses the unstable `public-dependency` feature.
-    //
-    // `setenv` might not be thread safe, so run it before using multiple threads.
-    env::set_var("RUSTC_BOOTSTRAP", "1");
+    // SAFETY: no other threads have been spawned
+    unsafe {
+        env::set_var("RUSTC_BOOTSTRAP", "1");
+    }
 
     let root_path: PathBuf = env::args_os().nth(1).expect("need path to root of repo").into();
     let cargo: PathBuf = env::args_os().nth(2).expect("need path to cargo").into();