diff --git a/index.js b/index.js
index aaf70f3..6dd75a0 100644
--- a/index.js
+++ b/index.js
@@ -3,66 +3,56 @@
 
 const {Readable: ReadableStream} = require('stream');
 
-const BUFFER = Symbol('buffer');
-const TYPE = Symbol('type');
+const wm = new WeakMap();
 
 class Blob {
-	constructor(...args) {
-		this[TYPE] = '';
-
-		const blobParts = args[0];
-		const options = args[1];
-
+	constructor(blobParts = [], options = {type: ''}) {
 		const buffers = [];
-		/* eslint-disable-next-line no-unused-vars */
 		let size = 0;
 
-		if (blobParts) {
-			blobParts.forEach(element => {
-				let buffer;
-				if (element instanceof Buffer) {
-					buffer = element;
-				} else if (ArrayBuffer.isView(element)) {
-					buffer = Buffer.from(element.buffer, element.byteOffset, element.byteLength);
-				} else if (element instanceof ArrayBuffer) {
-					buffer = Buffer.from(element);
-				} else if (element instanceof Blob) {
-					buffer = element[BUFFER];
-				} else {
-					buffer = Buffer.from(typeof element === 'string' ? element : String(element));
-				}
-
-				size += buffer.length;
-				buffers.push(buffer);
-			});
-		}
-
-		this[BUFFER] = Buffer.concat(buffers);
-
-		const type = options && options.type !== undefined && String(options.type).toLowerCase();
-		if (type && !/[^\u0020-\u007E]/.test(type)) {
-			this[TYPE] = type;
-		}
-
-		if (options && Buffer.isBuffer(options.buffer)) {
-			this[BUFFER] = options.buffer;
-		}
+		blobParts.forEach(element => {
+			let buffer;
+			if (element instanceof Buffer) {
+				buffer = element;
+			} else if (ArrayBuffer.isView(element)) {
+				buffer = Buffer.from(element.buffer, element.byteOffset, element.byteLength);
+			} else if (element instanceof ArrayBuffer) {
+				buffer = Buffer.from(element);
+			} else if (element instanceof Blob) {
+				buffer = wm.get(element).buffer;
+			} else {
+				buffer = Buffer.from(typeof element === 'string' ? element : String(element));
+			}
+
+			size += buffer.length;
+			buffers.push(buffer);
+		});
+
+		const buffer = Buffer.concat(buffers, size);
+
+		const type = options.type === undefined ? '' : String(options.type).toLowerCase();
+
+		wm.set(this, {
+			type: /[^\u0020-\u007E]/.test(type) ? '' : type,
+			size,
+			buffer
+		});
 	}
 
 	get size() {
-		return this[BUFFER].length;
+		return wm.get(this).size;
 	}
 
 	get type() {
-		return this[TYPE];
+		return wm.get(this).type;
 	}
 
 	text() {
-		return Promise.resolve(this[BUFFER].toString());
+		return Promise.resolve(wm.get(this).buffer.toString());
 	}
 
 	arrayBuffer() {
-		const buf = this[BUFFER];
+		const buf = wm.get(this).buffer;
 		const ab = buf.buffer.slice(buf.byteOffset, buf.byteOffset + buf.byteLength);
 		return Promise.resolve(ab);
 	}
@@ -70,7 +60,7 @@ class Blob {
 	stream() {
 		const readable = new ReadableStream();
 		readable._read = () => { };
-		readable.push(this[BUFFER]);
+		readable.push(wm.get(this).buffer);
 		readable.push(null);
 		return readable;
 	}
@@ -88,30 +78,29 @@ class Blob {
 		let relativeEnd;
 
 		if (start === undefined) {
-			relativeStart = 0;
+			relativeStart = 0; //
 		} else if (start < 0) {
-			relativeStart = Math.max(size + start, 0);
+			relativeStart = Math.max(size + start, 0); //
 		} else {
 			relativeStart = Math.min(start, size);
 		}
 
 		if (end === undefined) {
-			relativeEnd = size;
+			relativeEnd = size; //
 		} else if (end < 0) {
-			relativeEnd = Math.max(size + end, 0);
+			relativeEnd = Math.max(size + end, 0); //
 		} else {
 			relativeEnd = Math.min(end, size);
 		}
 
 		const span = Math.max(relativeEnd - relativeStart, 0);
-
-		const buffer = this[BUFFER];
-		const slicedBuffer = buffer.slice(
+		const slicedBuffer = wm.get(this).buffer.slice(
 			relativeStart,
 			relativeStart + span
 		);
 		const blob = new Blob([], {type: args[2]});
-		blob[BUFFER] = slicedBuffer;
+		const _ = wm.get(blob);
+		_.buffer = slicedBuffer;
 		return blob;
 	}
 }
diff --git a/test.js b/test.js
index a25be73..115835f 100644
--- a/test.js
+++ b/test.js
@@ -3,12 +3,32 @@ const Blob = require('.');
 const getStream = require('get-stream');
 const {Response} = require('node-fetch');
 
-test('Blob ctor', t => {
+test('new Blob()', t => {
+	const blob = new Blob(); // eslint-disable-line no-unused-vars
+	t.pass();
+});
+
+test('new Blob(parts)', t => {
 	const data = 'a=1';
 	const blob = new Blob([data]); // eslint-disable-line no-unused-vars
 	t.pass();
 });
 
+test('Blob ctor parts', async t => {
+	const parts = [
+		'a',
+		new Uint8Array([98]),
+		new Uint16Array([25699]),
+		new Uint8Array([101]).buffer,
+		Buffer.from('f'),
+		new Blob(['g']),
+		{}
+	];
+
+	const blob = new Blob(parts);
+	t.is(await blob.text(), 'abcdefg[object Object]');
+});
+
 test('Blob size', t => {
 	const data = 'a=1';
 	const blob = new Blob([data]);
@@ -16,12 +36,27 @@ test('Blob size', t => {
 });
 
 test('Blob type', t => {
-	const data = 'a=1';
 	const type = 'text/plain';
-	const blob = new Blob([data], {type});
+	const blob = new Blob([], {type});
+	t.is(blob.type, type);
+});
+
+test('Blob slice type', t => {
+	const type = 'text/plain';
+	const blob = new Blob().slice(0, 0, type);
 	t.is(blob.type, type);
 });
 
+test('invalid Blob type', t => {
+	const blob = new Blob([], {type: '\u001Ftext/plain'});
+	t.is(blob.type, '');
+});
+
+test('invalid Blob slice type', t => {
+	const blob = new Blob().slice(0, 0, '\u001Ftext/plain');
+	t.is(blob.type, '');
+});
+
 test('Blob text()', async t => {
 	const data = 'a=1';
 	const type = 'text/plain';
@@ -55,11 +90,27 @@ test('Blob toString()', t => {
 });
 
 test('Blob slice()', async t => {
-	const data = 'a=1';
-	const type = 'text/plain';
-	const blob = new Blob([data], {type});
-	const blob2 = blob.slice(0, 1);
-	t.is(await blob2.text(), data.slice(0, 1));
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice();
+	t.is(await blob.text(), data);
+});
+
+test('Blob slice(0, 1)', async t => {
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice(0, 1);
+	t.is(await blob.text(), 'a');
+});
+
+test('Blob slice(-1)', async t => {
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice(-1);
+	t.is(await blob.text(), 'h');
+});
+
+test('Blob slice(0, -1)', async t => {
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice(0, -1);
+	t.is(await blob.text(), 'abcdefg');
 });
 
 test('Blob works with node-fetch Response.blob()', async t => {