diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index e1b41e3..2e3b21e 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -20,9 +20,12 @@ jobs:
     steps:
       - name: Checkout the repository using git
         uses: actions/checkout@v4
-      - run: node --version
+      - name: Set node version
+        uses: actions/setup-node@v4
+        with:
+          node-version: '>=20'
       - name: Cache node modules
-        uses: actions/cache@v1
+        uses: actions/cache@v3
         with:
           path: ~/.npm
           key: ${{ runner.os }}-npm-${{ hashFiles('**/package-lock.json') }}
diff --git a/README.md b/README.md
index 1a2732f..c080431 100644
--- a/README.md
+++ b/README.md
@@ -40,7 +40,7 @@ It does not modify the ROM, it is only an explorer of the resources present in t
 
 ## Contribute
 
-To run it locally, clone the repo and install the dependencies:
+To run it locally, make sure that node v20 or higher is installed, clone the repo and install the dependencies:
 
 ```sh
 npm install
diff --git a/index.js b/index.js
index 0a03954..e6761df 100755
--- a/index.js
+++ b/index.js
@@ -9,7 +9,7 @@ import {
   isJapaneseVersion,
   getResFromCrc32,
 } from './src/lib/getResFromCrc32.js';
-import parseRom from './src/lib/parseRom.js';
+import parseRom from './src/lib/parser/parseRom.js';
 import { stringify } from './src/lib/cliUtils.js';
 
 const options = {
diff --git a/package.json b/package.json
index 739c7e9..460a3ef 100644
--- a/package.json
+++ b/package.json
@@ -23,8 +23,12 @@
   "bin": {
     "scumm-nes": "index.js"
   },
+  "engines": {
+    "node": ">=20"
+  },
   "scripts": {
     "test": "node --test",
+    "coverage": "node --experimental-test-coverage --test",
     "dev": "parcel",
     "start": "parcel",
     "build": "parcel build --public-url /scumm-nes"
diff --git a/src/App.js b/src/App.js
index 50853de..f671ba9 100644
--- a/src/App.js
+++ b/src/App.js
@@ -13,7 +13,7 @@ const App = () => {
   const navigate = useNavigate();
 
   const onFile = async (rom, res) => {
-    const { default: parseRom } = await import('./lib/parseRom');
+    const { default: parseRom } = await import('./lib/parser/parseRom');
     setRom(rom);
     setRes(res);
     setResources(parseRom(rom, res));
diff --git a/src/lib/parsePreps.js b/src/lib/parser/parsePreps.js
similarity index 100%
rename from src/lib/parsePreps.js
rename to src/lib/parser/parsePreps.js
diff --git a/src/lib/parseRom.js b/src/lib/parser/parseRom.js
similarity index 91%
rename from src/lib/parseRom.js
rename to src/lib/parser/parseRom.js
index 2301cee..12e3f4a 100644
--- a/src/lib/parseRom.js
+++ b/src/lib/parser/parseRom.js
@@ -1,5 +1,5 @@
-import parseRooms from '../lib/parseRooms.js';
-import parseRoomGfx from '../lib/parseRoomGfx.js';
+import parseRooms from './parseRooms.js';
+import parseRoomGfx from './parseRoomGfx.js';
 import parsePreps from './parsePreps.js';
 
 const parseRom = (arrayBuffer, res) => {
diff --git a/src/lib/parseRoomGfx.js b/src/lib/parser/parseRoomGfx.js
similarity index 100%
rename from src/lib/parseRoomGfx.js
rename to src/lib/parser/parseRoomGfx.js
diff --git a/src/lib/parseRooms.js b/src/lib/parser/parseRooms.js
similarity index 100%
rename from src/lib/parseRooms.js
rename to src/lib/parser/parseRooms.js
diff --git a/src/lib/parser.js b/src/lib/parser/parser.js
similarity index 84%
rename from src/lib/parser.js
rename to src/lib/parser/parser.js
index f389c78..eccc570 100644
--- a/src/lib/parser.js
+++ b/src/lib/parser/parser.js
@@ -3,8 +3,8 @@ class Parser {
   #ptr = 0;
   #characters = {};
 
-  constructor(arrayBuffer, characters = {}) {
-    this.#view = new DataView(arrayBuffer);
+  constructor(buffer, characters = {}) {
+    this.#view = new DataView(buffer);
     this.#characters = characters;
   }
 
@@ -25,7 +25,7 @@ class Parser {
       return 0x00;
     }
 
-    const char = String.fromCharCode(charCode);
+    const char = String.fromCodePoint(charCode);
 
     if (typeof this.#characters[char] !== 'undefined') {
       return this.#characters[char];
diff --git a/src/lib/serialiser/serialisePreps.js b/src/lib/serialiser/serialisePreps.js
new file mode 100644
index 0000000..a6449a4
--- /dev/null
+++ b/src/lib/serialiser/serialisePreps.js
@@ -0,0 +1,14 @@
+import Serialiser from './serialiser.js';
+
+const serialisePreps = (preps = [], characters = {}) => {
+  const serialiser = new Serialiser(characters);
+
+  for (let i = 0; i < preps.length; i++) {
+    serialiser.setString(preps[i]);
+    serialiser.setUint8(); // 0x00 is the default value.
+  }
+
+  return serialiser.buffer;
+};
+
+export default serialisePreps;
diff --git a/src/lib/serialiser/serialiser.js b/src/lib/serialiser/serialiser.js
new file mode 100644
index 0000000..3bb7a7f
--- /dev/null
+++ b/src/lib/serialiser/serialiser.js
@@ -0,0 +1,37 @@
+const maxByteLength = 16384; // The largest resource is sprdata.
+
+class Serialiser {
+  #view;
+  #ptr = 0;
+  #characters = {};
+
+  constructor(characters = {}) {
+    const buffer = new ArrayBuffer(0, { maxByteLength });
+    this.#view = new DataView(buffer);
+    // Swap keys for values.
+    this.#characters = Object.fromEntries(
+      Object.entries(characters).map(([key, value]) => [value, key]),
+    );
+  }
+
+  setUint8(value = 0x00) {
+    this.#view.buffer.resize(this.#ptr + 1);
+    this.#view.setUint8(this.#ptr++, value);
+  }
+
+  setString(str) {
+    // See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/codePointAt#looping_with_codepointat
+    for (let codePoint of str) {
+      if (this.#characters[codePoint] !== undefined) {
+        codePoint = this.#characters[codePoint];
+      }
+      this.setUint8(codePoint.codePointAt(0));
+    }
+  }
+
+  get buffer() {
+    return this.#view.buffer;
+  }
+}
+
+export default Serialiser;
diff --git a/test/parsePreps.test.js b/test/parsePreps.test.js
index 7e55d66..3f36684 100644
--- a/test/parsePreps.test.js
+++ b/test/parsePreps.test.js
@@ -1,6 +1,6 @@
 import { describe, it } from 'node:test';
 import assert from 'node:assert/strict';
-import parsePreps from '../src/lib/parsePreps.js';
+import parsePreps from '../src/lib/parser/parsePreps.js';
 
 describe('parsePreps', () => {
   it('should set the offset value in metadata.', () => {
@@ -39,7 +39,7 @@ describe('parsePreps', () => {
     view.setUint8(4, 'c'.codePointAt(0));
     view.setUint8(5, 0x00);
 
-    const characters = { a: '0', b: 1, c: '2' };
+    const characters = { a: '0', b: '1', c: '2' };
     const { preps } = parsePreps(buffer, 0, 0, characters);
     assert.deepEqual(preps, ['0', '1', '2']);
   });
diff --git a/test/serialisePreps.test.js b/test/serialisePreps.test.js
new file mode 100644
index 0000000..1eff6c6
--- /dev/null
+++ b/test/serialisePreps.test.js
@@ -0,0 +1,37 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import serialisePreps from '../src/lib/serialiser/serialisePreps.js';
+
+describe('serialisePreps', () => {
+  it('should return an instance of ArrayBuffer.', () => {
+    const buffer = serialisePreps();
+    assert.ok(buffer instanceof ArrayBuffer);
+  });
+
+  it('should serialise prepositions.', () => {
+    const preps = ['a', 'b', 'c'];
+    const buffer = serialisePreps(preps);
+    const view = new DataView(buffer);
+
+    assert.equal(view.getUint8(0), 0x61);
+    assert.equal(view.getUint8(1), 0x00);
+    assert.equal(view.getUint8(2), 0x62);
+    assert.equal(view.getUint8(3), 0x00);
+    assert.equal(view.getUint8(4), 0x63);
+    assert.equal(view.getUint8(5), 0x00);
+  });
+
+  it('should serialise characters according to the character mapping.', () => {
+    const preps = ['0', '1', '2'];
+    const characters = { a: '0', b: '1', c: '2' };
+    const buffer = serialisePreps(preps, characters);
+
+    const view = new DataView(buffer);
+    assert.equal(view.getUint8(0), 0x61);
+    assert.equal(view.getUint8(1), 0x00);
+    assert.equal(view.getUint8(2), 0x62);
+    assert.equal(view.getUint8(3), 0x00);
+    assert.equal(view.getUint8(4), 0x63);
+    assert.equal(view.getUint8(5), 0x00);
+  });
+});