Index: /home/lrbabe/workspace/jQuery/jquery/src/core.js =================================================================== --- /home/lrbabe/workspace/jQuery/jquery/src/core.js (revision 5654) +++ /home/lrbabe/workspace/jQuery/jquery/src/core.js (working copy) @@ -1098,7 +1098,7 @@ // Set the alpha filter to set the opacity elem.filter = (elem.filter || "").replace( /alpha\([^)]*\)/, "" ) + - (parseInt( value ) + '' == "NaN" ? "" : "alpha(opacity=" + value * 100 + ")"); + (isNaN(parseInt(value))? "" : "alpha(opacity=" + value * 100 + ")"); } return elem.filter && elem.filter.indexOf("opacity=") >= 0 ?