diff --git a/src/css.js b/src/css.js
index 4bf818e5..99cb7358 100644
--- a/src/css.js
+++ b/src/css.js
@@ -88,7 +88,11 @@ jQuery.extend({
 
 			// If a hook was provided, use that value, otherwise just set the specified value
 			if ( !hooks || !("set" in hooks) || (value = hooks.set( elem, value )) !== undefined ) {
-				style[ name ] = value;
+				// Wrapped to prevent IE from throwing errors when 'invalid' values are provided
+				// Fixes bug #5509
+				try {
+					style[ name ] = value;
+				} catch(e) {}
 			}
 
 		} else {
diff --git a/test/unit/css.js b/test/unit/css.js
index 468f7638..26dd7047 100644
--- a/test/unit/css.js
+++ b/test/unit/css.js
@@ -64,7 +64,7 @@ test("css(String|Hash)", function() {
 });
 
 test("css(String, Object)", function() {
-	expect(21);
+	expect(22);
 
 	ok( jQuery('#nothiddendiv').is(':visible'), 'Modifying CSS display: Assert element is visible');
 	jQuery('#nothiddendiv').css("display", 'none');
@@ -104,6 +104,16 @@ test("css(String, Object)", function() {
 
 	equals( ret, div, "Make sure setting undefined returns the original set." );
 	equals( div.css("display"), display, "Make sure that the display wasn't changed." );
+
+	// Test for Bug #5509
+	var success = true;
+	try {
+		jQuery('#foo').css("backgroundColor", "rgba(0, 0, 0, 0.1)");
+	}
+	catch (e) {
+		success = false;
+	}
+	ok( success, "Setting RGBA values does not throw Error" );
 });
 
 if(jQuery.browser.msie) {