CPF e CNPJ no mesmo campo

O que esta errado nesse código?

http://jsfiddle.net/ujrvLnax/

CPF/CMPJ: </label><input type="text" id="cpf_cnpj" />

jQuery(document).ready(function() {
 jQuery('#cpf_cnpj').mask("99.999.999/9999-99").ready(function(event) {
 var target, cpf_cnpj, element;
 target = (event.currentTarget) ? event.currentTarget : event.srcElement;
 cpf_cnpj = target.value.replace(/\D/g, '');
 element = $(target);
 element.unmask();
 if(cpf_cnpj.length > 11) {
 element.mask("99.999.999/9999-99");
 } else {
 element.mask("999.999.999-99");
 }
 });
});