diff --git a/src/index.js b/src/index.js
index c1f53ca..e7f0d4e 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,25 +1,25 @@
+const is = (val, type) => Object.prototype.toString.call(val) === `[object ${type}]`;
+
 function toVal(mix) {
 	var k, y, str='';
 
-	if (typeof mix === 'string' || typeof mix === 'number') {
+	if (is(mix, 'String') || is(mix, 'Number')) {
 		str += mix;
-	} else if (typeof mix === 'object') {
-		if (Array.isArray(mix)) {
+	} else if (is(mix, 'Array')) {
 			var len=mix.length;
 			for (k=0; k < len; k++) {
-				if (mix[k]) {
+				if (mix[k] && mix[k].valueOf()) {
 					if (y = toVal(mix[k])) {
 						str && (str += ' ');
 						str += y;
 					}
 				}
 			}
-		} else {
-			for (y in mix) {
-				if (mix[y]) {
-					str && (str += ' ');
-					str += y;
-				}
+	} else if (is(mix, 'Object')) {
+		for (y in mix) {
+			if (mix[y] && mix[y].valueOf()) {
+				str && (str += ' ');
+				str += y;
 			}
 		}
 	}
@@ -30,7 +30,7 @@ function toVal(mix) {
 export function clsx() {
 	var i=0, tmp, x, str='', len=arguments.length;
 	for (; i < len; i++) {
-		if (tmp = arguments[i]) {
+		if ((tmp = arguments[i]) && tmp.valueOf()) {
 			if (x = toVal(tmp)) {
 				str && (str += ' ');
 				str += x
diff --git a/src/lite.js b/src/lite.js
index c1e9364..6a98fef 100644
--- a/src/lite.js
+++ b/src/lite.js
@@ -2,7 +2,7 @@ export function clsx() {
 	var i=0, tmp, str='', len=arguments.length;
 	for (; i < len; i++) {
 		if (tmp = arguments[i]) {
-			if (typeof tmp === 'string') {
+			if (Object.prototype.toString.call(tmp) === '[object String]') {
 				str += (str && ' ') + tmp;
 			}
 		}
diff --git a/test/index.js b/test/index.js
index 5fd9dec..9ae8c08 100644
--- a/test/index.js
+++ b/test/index.js
@@ -28,6 +28,20 @@ test('strings (variadic)', () => {
 	assert.is(fn(false && 'foo', 'bar', 'baz', ''), 'bar baz');
 });
 
+test('string instances', () => {
+	assert.is(fn(new String('')), '');
+	assert.is(fn(new String('foo')), 'foo');
+	assert.is(fn(true && new String('foo')), 'foo');
+	assert.is(fn(false && new String('foo')), '');
+});
+
+test('string instances (variadic)', () => {
+	assert.is(fn(new String('')), '');
+	assert.is(fn(new String('foo'), new String('bar')), 'foo bar');
+	assert.is(fn(true && new String('foo'), false && new String('bar'), new String('baz')), 'foo baz');
+	assert.is(fn(false && new String('foo'), new String('bar'), new String('baz'), ''), 'bar baz');
+});
+
 test('numbers', () => {
 	assert.is(fn(1), '1');
 	assert.is(fn(12), '12');
@@ -43,6 +57,21 @@ test('numbers (variadic)', () => {
 	assert.is(fn(1, 2), '1 2');
 });
 
+test('number instances', () => {
+	assert.is(fn(new Number(1)), '1');
+	assert.is(fn(new Number(12)), '12');
+	assert.is(fn(new Number(0.1)), '0.1');
+	assert.is(fn(new Number(0)), '');
+
+	assert.is(fn(new Number(Infinity)), 'Infinity');
+	assert.is(fn(new Number(NaN)), '');
+});
+
+test('number instances (variadic)', () => {
+	assert.is(fn(new Number(0), new Number(1)), '1');
+	assert.is(fn(new Number(1), new Number(2)), '1 2');
+});
+
 test('objects', () => {
 	assert.is(fn({}), '');
 	assert.is(fn({ foo:true }), 'foo');
diff --git a/test/lite.js b/test/lite.js
index 157962b..67f64d3 100644
--- a/test/lite.js
+++ b/test/lite.js
@@ -28,6 +28,20 @@ test('strings (variadic)', () => {
 	assert.is(fn(false && 'foo', 'bar', 'baz', ''), 'bar baz');
 });
 
+test('string instances', () => {
+	assert.is(fn(new String('')), '');
+	assert.is(fn(new String('foo')), 'foo');
+	assert.is(fn(true && new String('foo')), 'foo');
+	assert.is(fn(false && new String('foo')), '');
+});
+
+test('string instances (variadic)', () => {
+	assert.is(fn(new String('')), '');
+	assert.is(fn(new String('foo'), new String('bar')), 'foo bar');
+	assert.is(fn(true && new String('foo'), false && new String('bar'), new String('baz')), 'foo baz');
+	assert.is(fn(false && new String('foo'), new String('bar'), new String('baz'), ''), 'bar baz');
+});
+
 test('emptys', () => {
 	assert.is(fn(''), '');
 	assert.is(fn(undefined), '');