diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 342743d21340f..043fe7a72c50f 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -1,9 +1,9 @@
 //! Checks the licenses of third-party dependencies.
 
-use std::collections::{HashMap, HashSet};
+use std::collections::{BTreeSet, HashMap, HashSet};
 use std::fmt::{Display, Formatter};
-use std::fs::{File, read_dir};
-use std::io::Write;
+use std::fs::{self, read_dir};
+use std::io;
 use std::path::Path;
 
 use cargo_metadata::semver::Version;
@@ -11,9 +11,6 @@ use cargo_metadata::{Metadata, Package, PackageId};
 
 use crate::diagnostics::{RunningCheck, TidyCtx};
 
-#[path = "../../../bootstrap/src/utils/proc_macro_deps.rs"]
-mod proc_macro_deps;
-
 #[derive(Clone, Copy)]
 struct ListLocation {
     path: &'static str,
@@ -722,53 +719,58 @@ fn check_proc_macro_dep_list(root: &Path, cargo: &Path, bless: bool, check: &mut
     }
     // Remove the proc-macro crates themselves
     proc_macro_deps.retain(|pkg| !is_proc_macro_pkg(&metadata[pkg]));
+    // Sort and deduplicate the crate names.
+    let proc_macro_deps =
+        proc_macro_deps.into_iter().map(|dep| metadata[dep].name.as_ref()).collect::<BTreeSet<_>>();
 
-    let proc_macro_deps: HashSet<_> =
-        proc_macro_deps.into_iter().map(|dep| metadata[dep].name.as_ref()).collect();
-    let expected = proc_macro_deps::CRATES.iter().copied().collect::<HashSet<_>>();
-
-    let needs_blessing = proc_macro_deps.difference(&expected).next().is_some()
-        || expected.difference(&proc_macro_deps).next().is_some();
+    let expected = {
+        use std::fmt::Write;
 
-    if needs_blessing && bless {
-        let mut proc_macro_deps: Vec<_> = proc_macro_deps.into_iter().collect();
-        proc_macro_deps.sort();
-        let mut file = File::create(root.join("src/bootstrap/src/utils/proc_macro_deps.rs"))
-            .expect("`proc_macro_deps` should exist");
-        writeln!(
-            &mut file,
-            "/// Do not update manually - use `./x.py test tidy --bless`
+        const HEADER: &str = "\
+/// Do not update manually - use `./x.py test tidy --bless`
 /// Holds all direct and indirect dependencies of proc-macro crates in tree.
 /// See <https://github.com/rust-lang/rust/issues/134863>
 pub static CRATES: &[&str] = &[
-    // tidy-alphabetical-start"
-        )
-        .unwrap();
+    // tidy-alphabetical-start
+";
+        const FOOTER: &str = "    // tidy-alphabetical-end
+];
+";
+
+        let mut buf = String::with_capacity(4096);
+        buf.push_str(HEADER);
         for dep in proc_macro_deps {
-            writeln!(&mut file, "    {dep:?},").unwrap();
+            writeln!(buf, "    {dep:?},").unwrap();
         }
-        writeln!(
-            &mut file,
-            "    // tidy-alphabetical-end
-];"
-        )
-        .unwrap();
-    } else {
-        let mut error_found = false;
+        buf.push_str(FOOTER);
+        buf
+    };
 
-        for missing in proc_macro_deps.difference(&expected) {
-            error_found = true;
-            check.error(format!(
-                "proc-macro crate dependency `{missing}` is not registered in `src/bootstrap/src/utils/proc_macro_deps.rs`",
-            ));
-        }
-        for extra in expected.difference(&proc_macro_deps) {
-            error_found = true;
-            check.error(format!(
-                "`{extra}` is registered in `src/bootstrap/src/utils/proc_macro_deps.rs`, but is not a proc-macro crate dependency",
-            ));
+    const PROC_MACRO_DEPS_RS: &str = "src/bootstrap/src/utils/proc_macro_deps.rs";
+    let proc_macro_deps_rs_path = &root.join(PROC_MACRO_DEPS_RS);
+    let actual = match fs::read_to_string(proc_macro_deps_rs_path) {
+        Ok(actual) => actual,
+        Err(e) => {
+            if e.kind() == io::ErrorKind::NotFound {
+                check.error(format!(
+                    "`{PROC_MACRO_DEPS_RS}` not found; has it been moved or renamed?"
+                ));
+            } else {
+                check.error(format!("`{PROC_MACRO_DEPS_RS}` could not be read: {e:?}"));
+            }
+            return;
         }
-        if error_found {
+    };
+
+    if actual != expected {
+        if bless {
+            fs::write(proc_macro_deps_rs_path, &expected).unwrap();
+        } else {
+            let diff = similar::TextDiff::from_lines(&actual, &expected);
+            let mut unified = diff.unified_diff();
+            unified.header(PROC_MACRO_DEPS_RS, "(expected)");
+
+            check.error(format!("`{PROC_MACRO_DEPS_RS}` is not up-to-date:\n{unified}"));
             check.message("Run `./x.py test tidy --bless` to regenerate the list");
         }
     }