diff --git a/src/index.js b/src/index.js
index 419ddee..493dc4e 100644
--- a/src/index.js
+++ b/src/index.js
@@ -19,9 +19,25 @@ export default function klona(x) {
 		return tmp;
 	}
 
-	if (str === '[object Set]') return new Set(x);
-	if (str === '[object Date]') return new Date(+x);
-	if (str === '[object Map]') return new Map(x);
+	if (str === '[object Set]') {
+		tmp = new Set();
+		x.forEach(function (val) {
+			tmp.add(klona(val));
+		});
+		return tmp;
+	}
+
+	if (str === '[object Map]') {
+		tmp = new Map();
+		x.forEach(function (val, key) {
+			tmp.set(key, klona(val));
+		});
+		return tmp;
+	}
+
+	if (str === '[object Date]') {
+		return new Date(+x);
+	}
 
 	if (str === '[object RegExp]') {
 		tmp = new RegExp(x.source, x.flags);
diff --git a/test/index.js b/test/index.js
index 86d1a2e..634516e 100644
--- a/test/index.js
+++ b/test/index.js
@@ -138,7 +138,7 @@ test('function', t => {
 });
 
 
-test('map', t => {
+test('map :: flat', t => {
 	const input = new Map();
 	const output = klona(input);
 
@@ -154,6 +154,28 @@ test('map', t => {
 });
 
 
+test('map :: nested', t => {
+	const input = new Map([
+		['foo', { a: 1 }],
+		['bar', [1, 2, 3]],
+	]);
+	const output = klona(input);
+
+	const foo = output.get('foo');
+	foo.b = 2;
+	foo.a++;
+
+	t.deepEqual(input.get('foo'), { a: 1 });
+	t.deepEqual(output.get('foo'), { a: 2, b: 2 });
+
+	output.get('bar').push(4, 5, 6);
+	t.deepEqual(input.get('bar'), [1, 2, 3]);
+	t.deepEqual(output.get('bar'), [1, 2, 3, 4, 5, 6]);
+
+	t.end();
+});
+
+
 test('null', t => {
 	let input = null;
 	let output = klona(input);
@@ -264,7 +286,7 @@ test('regexp :: state', t => {
 });
 
 
-test('set', t => {
+test('set :: flat', t => {
 	const input = new Set('hello');
 	const output = klona(input);
 
@@ -279,6 +301,22 @@ test('set', t => {
 	t.end();
 });
 
+test('set :: nested', t => {
+	const input = new Set([{ foo: 123 }]);
+	const output = klona(input);
+
+	t.deepEqual(input, output);
+
+	const [obj] = [...output.keys()];
+	obj.bar = 456;
+	obj.foo++;
+
+	const [item] = [...input.keys()];
+	t.deepEqual(item, { foo: 123 });
+
+	t.end();
+});
+
 
 test('string', t => {
 	let input = 'hello';