diff --git a/src/css.js b/src/css.js
index 17ac136b..d23549fa 100644
--- a/src/css.js
+++ b/src/css.js
@@ -7,6 +7,8 @@ var ralpha = /alpha\([^)]*\)/i,
 	rupper = /([A-Z]|^ms)/g,
 	rnumpx = /^-?\d+(?:px)?$/i,
 	rnum = /^-?\d/,
+	rrelNum = /=/,
+	rrelString = /[^+\-\de]+/g,
 
 	cssShow = { position: "absolute", visibility: "hidden", display: "block" },
 	cssWidth = [ "Left", "Right" ],
@@ -75,7 +77,7 @@ jQuery.extend({
 		}
 
 		// Make sure that we're working with the right name
-		var ret, origName = jQuery.camelCase( name ),
+		var ret, parsed, type, origName = jQuery.camelCase( name ),
 			style = elem.style, hooks = jQuery.cssHooks[ origName ];
 
 		name = jQuery.cssProps[ origName ] || origName;
@@ -87,6 +89,12 @@ jQuery.extend({
 				return;
 			}
 
+			// convert string to number or relative number
+			if ( type === "string" ) {
+				parsed = +value.replace( rrelString, '' );
+				value = rrelNum.test( value ) ? parsed + jQuery.css( elem, name ) : parsed;
+			}
+
 			// If a number was passed in, add 'px' to the (except for certain CSS properties)
 			if ( typeof value === "number" && !jQuery.cssNumber[ origName ] ) {
 				value += "px";
diff --git a/test/unit/css.js b/test/unit/css.js
index 8ae8fcb3..c4724fcd 100644
--- a/test/unit/css.js
+++ b/test/unit/css.js
@@ -105,6 +105,27 @@ test("css(String|Hash)", function() {
 	equals( child[0].style.fontSize, old, "Make sure font-size isn't changed on null." );
 });
 
+test("css() explicit and relative values", function() {
+	var $elem = jQuery('#nothiddendiv');
+	
+	$elem.css({ width: 1, height: 1 });
+	ok( [$elem.width(), $elem.height()], [1,1] );
+	$elem.css({ width: "+=9", height: "+=9" });
+	ok( [$elem.width(), $elem.height()], [10,10] );
+	$elem.css({ width: "-=9", height: "-=9" });
+	ok( [$elem.width(), $elem.height()], [1,1] );
+	$elem.css({ width: "+=9px", height: "+=9px" });
+	ok( [$elem.width(), $elem.height()], [10,10] );
+	$elem.css({ width: "-=9px", height: "-=9px" });
+	ok( [$elem.width(), $elem.height()], [1,1] );
+	$elem.css("width", "+=9").css("height", "+=9");
+	ok( [$elem.width(), $elem.height()], [10,10] );
+	$elem.css("width", "+9").css("height", "+9");
+	ok( [$elem.width(), $elem.height()], [9,9] );
+	$elem.css("width", "-9").css("height", "-9");
+	ok( [$elem.width(), $elem.height()], [0,0] );
+});
+
 test("css(String, Object)", function() {
 	expect(22);