diff --git a/lib/build.js b/lib/build.js
index 062a4824e..80141af98 100644
--- a/lib/build.js
+++ b/lib/build.js
@@ -25,6 +25,7 @@ const OptimizeJs = require('./optimize-js');
 const RemoteTemplate = require('./remote-template');
 const Spinner = require('./spinner');
 const TemplateDependencies = require('./template-dependencies');
+const {unique} = require('./utils');
 
 const templateSrc = path.join(__dirname, '../template/src');
 const parseElmFolder = path.join(__dirname, '../parseElm');
@@ -354,15 +355,6 @@ function updateSourceDirectories(options, userSrc, elmJson) {
   };
 }
 
-/**
- * @template T
- * @param {T[]} array
- * @returns {T[]}
- */
-function unique(array) {
-  return [...new Set(array)];
-}
-
 async function compileElmProject(
   options,
   dest,
diff --git a/lib/extra-files.js b/lib/extra-files.js
index e18aa74e6..283bc4f05 100644
--- a/lib/extra-files.js
+++ b/lib/extra-files.js
@@ -4,6 +4,7 @@
 const {glob} = require('tinyglobby');
 const FS = require('./fs-wrapper');
 const OsHelpers = require('./os-helpers');
+const {unique} = require('./utils');
 
 /**
  * Collect the extra files requested by the rules.
@@ -15,8 +16,7 @@ async function collect(requests) {
   const files2D = await Promise.all(
     requests.map(async (request) => await getFiles(request))
   );
-  const flatFiles = files2D.flat();
-  const files = unique(flatFiles);
+  const files = unique(files2D.flat());
 
   const filesAndContents = await Promise.all(
     files.map(async (filePath) => {
@@ -56,15 +56,6 @@ async function getFiles(request) {
   );
 }
 
-/**
- * @template T
- * @param {T[]} array
- * @returns {T[]}
- */
-function unique(array) {
-  return [...new Set(array)];
-}
-
 module.exports = {
   collect
 };
diff --git a/lib/os-helpers.js b/lib/os-helpers.js
index 53d79af01..fefcab9f7 100644
--- a/lib/os-helpers.js
+++ b/lib/os-helpers.js
@@ -3,11 +3,11 @@
 /** @import {Path} from './types/path'; */
 
 /**
- * @param {Path} path_
+ * @param {Path} path
  * @returns {Path}
  */
-function makePathOsAgnostic(path_) {
-  return path_.replace(/.:/, '').replace(/\\/g, '/');
+function makePathOsAgnostic(path) {
+  return path.replace(/.:/, '').replace(/\\/g, '/');
 }
 
 module.exports = {
diff --git a/lib/parse-elm-worker.js b/lib/parse-elm-worker.js
index fa30039d0..4293dbb4b 100644
--- a/lib/parse-elm-worker.js
+++ b/lib/parse-elm-worker.js
@@ -46,7 +46,6 @@ function workerParseElm({source, elmParserPath}) {
   return promisifyPort({
     subscribeTo: app.ports.parseResult,
     sendThrough: app.ports.requestParsing,
-    // @ts-expect-error(TS2322): TS wants an `ElmJson`, but we're giving a string.
     data: source
   });
 }
diff --git a/lib/result-cache-json.js b/lib/result-cache-json.js
index 7f24a4d8f..01ff6cafd 100644
--- a/lib/result-cache-json.js
+++ b/lib/result-cache-json.js
@@ -109,13 +109,13 @@ function reviver(_, value_) {
   }
 }
 
-const _ListNilPROD = /** @type {const} */ ({$: 0});
+/** @type {ValueStruct} */
+const _ListNilPROD = {$: 0};
 
 /**
  * @param {string | string[]} array
  */
 function _ListFromArrayPROD(array) {
-  /** @type {ValueStruct} */
   let out = _ListNilPROD;
   for (let i = array.length; i--; ) {
     out = {$: 1, a: array[i], b: out};
diff --git a/lib/types/elm-internals.ts b/lib/types/elm-internals.ts
index 2a54ffd55..b503d55fe 100644
--- a/lib/types/elm-internals.ts
+++ b/lib/types/elm-internals.ts
@@ -1,7 +1,7 @@
 export type Value = null | ValueStruct | number | string;
 export type ValueStruct = {
-  $: 1 | -1 | 0 | `$L`;
-  a?: string[] | string;
-  b?: ValueStruct;
-  c?: unknown;
+  readonly $: 1 | -1 | 0 | `$L`;
+  readonly a?: string[] | string;
+  readonly b?: ValueStruct;
+  readonly c?: unknown;
 };
diff --git a/lib/types/parse-elm.ts b/lib/types/parse-elm.ts
index cd8cb9fb1..24269c9f3 100644
--- a/lib/types/parse-elm.ts
+++ b/lib/types/parse-elm.ts
@@ -1,4 +1,4 @@
-import {ElmFile, Source, type ElmJson} from './content.js';
+import {ElmFile, Source} from './content.js';
 import {Path} from './path.js';
 import type {SendPort, SubscribePort} from './promisify-port.js';
 
@@ -18,6 +18,6 @@ export type ParserApp = {
 };
 
 type ParserPorts = {
-  requestParsing: SendPort<ElmJson>;
+  requestParsing: SendPort<string>;
   parseResult: SubscribePort<ElmFile>;
 };
diff --git a/lib/utils.js b/lib/utils.js
new file mode 100644
index 000000000..c1966d1d9
--- /dev/null
+++ b/lib/utils.js
@@ -0,0 +1,12 @@
+/**
+ * @template T
+ * @param {T[]} array
+ * @returns {T[]}
+ */
+function unique(array) {
+  return [...new Set(array)];
+}
+
+module.exports = {
+  unique
+};