diff --git a/src/core.js b/src/core.js
index 7f30edea2..e28c1b524 100644
--- a/src/core.js
+++ b/src/core.js
@@ -483,8 +483,8 @@ jQuery.extend({
 		return obj && typeof obj === "object" && "setInterval" in obj;
 	},
 
-	isNaN: function( obj ) {
-		return obj == null || !rdigit.test( obj ) || isNaN( obj );
+	isNumeric: function( obj ) {
+		return obj != null && rdigit.test( obj ) && !isNaN( obj );
 	},
 
 	type: function( obj ) {
diff --git a/src/css.js b/src/css.js
index 76c2255ce..2adfdffe1 100644
--- a/src/css.js
+++ b/src/css.js
@@ -211,7 +211,7 @@ if ( !jQuery.support.opacity ) {
 		set: function( elem, value ) {
 			var style = elem.style,
 				currentStyle = elem.currentStyle,
-				opacity = jQuery.isNaN( value ) ? "" : "alpha(opacity=" + value * 100 + ")",
+				opacity = jQuery.isNumeric( value ) ? "alpha(opacity=" + value * 100 + ")" : "",
 				filter = currentStyle && currentStyle.filter || style.filter || "";
 
 			// IE has trouble with opacity if it does not have layout
diff --git a/src/data.js b/src/data.js
index 0ce3b7d66..02f96a849 100644
--- a/src/data.js
+++ b/src/data.js
@@ -323,7 +323,7 @@ function dataAttr( elem, key, data ) {
 				data = data === "true" ? true :
 				data === "false" ? false :
 				data === "null" ? null :
-				!jQuery.isNaN( data ) ? parseFloat( data ) :
+				jQuery.isNumeric( data ) ? parseFloat( data ) :
 					rbrace.test( data ) ? jQuery.parseJSON( data ) :
 					data;
 			} catch( e ) {}
diff --git a/src/dimensions.js b/src/dimensions.js
index 7df0d5ddf..d339817c9 100644
--- a/src/dimensions.js
+++ b/src/dimensions.js
@@ -61,7 +61,7 @@ jQuery.each([ "Height", "Width" ], function( i, name ) {
 			var orig = jQuery.css( elem, type ),
 				ret = parseFloat( orig );
 
-			return jQuery.isNaN( ret ) ? orig : ret;
+			return jQuery.isNumeric( ret ) ? ret : orig;
 
 		// Set the width or height on the element (default to pixels if value is unitless)
 		} else {
diff --git a/test/unit/core.js b/test/unit/core.js
index 0f4504a13..0756e7947 100644
--- a/test/unit/core.js
+++ b/test/unit/core.js
@@ -454,6 +454,46 @@ test("isFunction", function() {
 	});
 });
 
+test( "isNumeric", function() {
+	expect( 33 );
+
+	var t = jQuery.isNumeric;
+
+	ok( t("-10"), "Negative integer string");
+	ok( t("0"), "Zero string");
+	ok( t("5"), "Positive integer string");
+	ok( t(-16), "Negative integer number");
+	ok( t(0), "Zero integer number");
+	ok( t(32), "Positive integer number");
+	ok( t("040"), "Octal integer literal string");
+	ok( t(0144), "Octal integer literal");
+	ok( t("0xFF"), "Hexadecimal integer literal string");
+	ok( t(0xFFF), "Hexadecimal integer literal");
+	ok( t("-1.6"), "Negative floating point string");
+	ok( t("4.536"), "Positive floating point string");
+	ok( t(-2.6), "Negative floating point number");
+	ok( t(3.1415), "Positive floating point number");
+	ok( t(8e5), "Exponential notation");
+	ok( t("123e-2"), "Exponential notation string");
+	equals( t(""), false, "Empty string");
+	equals( t("        "), false, "Whitespace characters string");
+	equals( t("\t\t"), false, "Tab characters string");
+	equals( t("abcdefghijklm1234567890"), false, "Alphanumeric character string");
+	equals( t("xabcdefx"), false, "Non-numeric character string");
+	equals( t(true), false, "Boolean true literal");
+	equals( t(false), false, "Boolean false literal");
+	equals( t("bcfed5.2"), false, "Number with preceding non-numeric characters");
+	equals( t("7.2acdgs"), false, "Number with trailling non-numeric characters");
+	equals( t(undefined), false, "Undefined value");
+	equals( t(null), false, "Null value");
+	equals( t(NaN), false, "NaN value");
+	equals( t(Infinity), false, "Infinity primitive");
+	equals( t(Number.POSITIVE_INFINITY), false, "Positive Infinity");
+	equals( t(Number.NEGATIVE_INFINITY), false, "Negative Infinity");
+	equals( t({}), false, "Empty object");
+	equals( t(function(){} ), false, "Instance of a function");
+});
+
 test("isXMLDoc - HTML", function() {
 	expect(4);