diff --git src/core.js src/core.js
index 93f04ec..9f9eefb 100644
--- src/core.js
+++ src/core.js
@@ -313,10 +313,16 @@ jQuery.extend = jQuery.fn.extend = function() {
 					continue;
 				}
 
-				// Recurse if we're merging object literal values
-				if ( deep && copy && jQuery.isPlainObject(copy) ) {
-					// Don't extend not object literals
-					var clone = src && jQuery.isPlainObject(src) ? src : {};
+				// Recurse if we're merging object literal values or arrays
+				if ( deep && copy && ( jQuery.isPlainObject(copy) || jQuery.isArray(copy) ) ) {
+					var clone = {};
+					// Only extend object literals or arrays
+					if ( src && ( jQuery.isPlainObject(src) || jQuery.isArray(src) ) ) {
+						clone = src;
+					// Don't clone an array with an object
+					} else if ( jQuery.isArray (copy) ) {
+						clone = [];
+					}
 
 					// Never move original objects, clone them
 					target[ name ] = jQuery.extend( deep, clone, copy );
diff --git test/unit/core.js test/unit/core.js
index e3adc60..c779e28 100644
--- test/unit/core.js
+++ test/unit/core.js
@@ -657,7 +657,7 @@ test("jQuery.merge()", function() {
 });
 
 test("jQuery.extend(Object, Object)", function() {
-	expect(25);
+	expect(27);
 
 	var settings = { xnumber1: 5, xnumber2: 7, xstring1: "peter", xstring2: "pan" },
 		options = { xnumber2: 1, xstring2: "x", xxx: "newstring" },
@@ -667,7 +667,9 @@ test("jQuery.extend(Object, Object)", function() {
 		deep1copy = { foo: { bar: true } },
 		deep2 = { foo: { baz: true }, foo2: document },
 		deep2copy = { foo: { baz: true }, foo2: document },
-		deepmerged = { foo: { bar: true, baz: true }, foo2: document };
+		deepmerged = { foo: { bar: true, baz: true }, foo2: document },
+		arr = [1, 2, 3],
+		nestedarray = { arr: arr };
 
 	jQuery.extend(settings, options);
 	same( settings, merged, "Check if extended: settings must be extended" );
@@ -682,6 +684,9 @@ test("jQuery.extend(Object, Object)", function() {
 	same( deep2.foo, deep2copy.foo, "Check if not deep2: options must not be modified" );
 	equals( deep1.foo2, document, "Make sure that a deep clone was not attempted on the document" );
 
+	ok( jQuery.extend(true, [], arr) !== arr, "Deep extend of array must clone array" );
+	ok( jQuery.extend(true, {}, nestedarray).arr !== arr, "Deep extend of object must clone child array" );
+
 	var empty = {};
 	var optionsWithLength = { foo: { length: -1 } };
 	jQuery.extend(true, empty, optionsWithLength);