Error on loadXML function on ActiveXObject when xml string containg tag with attirbute that have not value

I want to load xml string into ActiveXObject in IE. I write this code:

var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
var flag = xmlDoc.loadXML("<a attr></a>");

attr is an attribute that have not value. But after run flag is false. How can I solve this problem?