diff --git a/package.json b/package.json
index c58b84d..99a44e4 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "typed-binary",
-  "version": "4.0.0",
+  "version": "4.0.1",
   "description": "Describe binary structures with full TypeScript support. Encode and decode into pure JavaScript objects.",
   "packageManager": "pnpm@8.15.8+sha256.691fe176eea9a8a80df20e4976f3dfb44a04841ceb885638fe2a26174f81e65e",
   "main": "dist/cjs/index.js",
@@ -10,7 +10,7 @@
     "check": "biome check --write .",
     "build": "rollup -c",
     "prepublishOnly": "pnpm lint && pnpm build",
-    "dryPublish": "npm publish --dry-run",
+    "dryPublish": "pnpm publish --dry-run",
     "test": "vitest run",
     "dev:test": "vitest",
     "ts-version": "tsc -v",
diff --git a/src/io/bufferIOBase.ts b/src/io/bufferIOBase.ts
index 5a42ed5..692912a 100644
--- a/src/io/bufferIOBase.ts
+++ b/src/io/bufferIOBase.ts
@@ -5,11 +5,11 @@ export type BufferIOOptions = {
   /**
    * @default 0
    */
-  byteOffset: number;
+  byteOffset?: number;
   /**
    * @default 'system'
    */
-  endianness: Endianness | 'system';
+  endianness?: Endianness | 'system';
 };
 
 export class BufferIOBase {
@@ -25,7 +25,13 @@ export class BufferIOBase {
   public readonly endianness: Endianness;
 
   constructor(buffer: ArrayBufferLike, options?: BufferIOOptions) {
-    this.byteOffset = options?.byteOffset ?? 0;
+    const { byteOffset = 0, endianness = 'system' } = options ?? {};
+
+    this.byteOffset = byteOffset;
+
+    const systemEndianness = getSystemEndianness();
+    this.endianness = endianness === 'system' ? systemEndianness : endianness;
+    this.switchEndianness = this.endianness !== systemEndianness;
 
     let innerBuffer = buffer;
     if (typeof Buffer !== 'undefined' && innerBuffer instanceof Buffer) {
@@ -41,15 +47,6 @@ export class BufferIOBase {
     this.helperUint32View = new Uint32Array(helperBuffer);
     this.helperFloatView = new Float32Array(helperBuffer);
     this.helperByteView = new Uint8Array(helperBuffer);
-
-    const systemEndianness = getSystemEndianness();
-
-    this.endianness =
-      !options || options.endianness === 'system'
-        ? systemEndianness
-        : options.endianness;
-
-    this.switchEndianness = this.endianness !== systemEndianness;
   }
 
   get currentByteOffset() {
diff --git a/src/io/bufferReaderWriter.test.ts b/src/io/bufferReaderWriter.test.ts
index bb7d532..80868a8 100644
--- a/src/io/bufferReaderWriter.test.ts
+++ b/src/io/bufferReaderWriter.test.ts
@@ -1,9 +1,30 @@
 import { describe, expect, it } from 'vitest';
 import { randBetween, randIntBetween } from '../test/random';
+import { getSystemEndianness } from '../util';
 import { BufferReader } from './bufferReader';
 import { BufferWriter } from './bufferWriter';
 
 describe('BufferWriter/BufferReader', () => {
+  it('parses options correctly', () => {
+    const buffer = Buffer.alloc(16);
+
+    const noOptions = new BufferWriter(buffer);
+    expect(noOptions.endianness).toEqual(getSystemEndianness());
+    expect(noOptions.currentByteOffset).toEqual(0);
+
+    const withByteOffset = new BufferWriter(buffer, { byteOffset: 16 });
+    expect(withByteOffset.endianness).toEqual(getSystemEndianness());
+    expect(withByteOffset.currentByteOffset).toEqual(16);
+
+    const withBigEndian = new BufferWriter(buffer, { endianness: 'big' });
+    expect(withBigEndian.endianness).toEqual('big');
+    expect(withBigEndian.currentByteOffset).toEqual(0);
+
+    const withLittleEndian = new BufferWriter(buffer, { endianness: 'little' });
+    expect(withLittleEndian.endianness).toEqual('little');
+    expect(withLittleEndian.currentByteOffset).toEqual(0);
+  });
+
   it('should encode and decode int sequence', () => {
     // Generating random int sequence
     const intList = [];