diff --git a/src/css/curCSS.js b/src/css/curCSS.js
index b648b8dca..c30519d3d 100644
--- a/src/css/curCSS.js
+++ b/src/css/curCSS.js
@@ -44,7 +44,9 @@ function curCSS( elem, name, computed ) {
 		}
 	}
 
-	return ret;
+	// Support: IE
+	// IE returns zIndex value as an integer.
+	return ret === undefined ? ret : ret + "";
 }
 
 return curCSS;
diff --git a/test/unit/css.js b/test/unit/css.js
index 460e5d60b..cd70adbfc 100644
--- a/test/unit/css.js
+++ b/test/unit/css.js
@@ -197,6 +197,16 @@ test( "css() explicit and relative values", 29, function() {
 	equal( $elem.css("opacity"), "1", "'+=0.5' on opacity (params)" );
 });
 
+test("css(String) where values are z-index", function() {
+	expect(1);
+
+	var $elem = jQuery( "<div>" ).appendTo( "#qunit-fixture" );
+
+	$elem.css({ "position": "absolute", "z-index": "1000" });
+	strictEqual( $elem.css( "z-index" ), "1000" );
+});
+
+
 test("css(String, Object)", function() {
 	expect( 19 );
 	var j, div, display, ret, success;
@@ -353,6 +363,14 @@ test("css(Object) where values are Functions", function() {
 	jQuery("#cssFunctionTest").remove();
 });
 
+test("css(String) where values are undefined", function() {
+	expect(1);
+
+	var $elem = jQuery( "#nothiddendiv" );
+
+	strictEqual( $elem.css( "test" ), undefined );
+});
+
 test("css(Object) where values are Functions with incoming values", function() {
 	expect(3);