Check is a specific form field is valid

I've been searching for a while now and haven't found a solution yet.

I'm an ASP.NET and MVC4/Razor2 newbie, so I'm mostly editing the default project.

Anyway, my issue is that I'm using Twitter Bootstrap and I need to add an error CSS class on a div if the under-laying field is not valid.

So far I have this:

    <div class="control-group error">
      @Html.LabelFor(m => m.Password, new { @class = "control-label" })
      <div class="controls">
        @Html.PasswordFor(m => m.Password)
        @Html.ValidationMessageFor(m => m.Password, null, new { @class = "inline-help error" })
      </div>
    </div>

What should I do to make Razor insert the error class in the first div of my snippet when the field is invalid.

UPDATE: I found a way to do it, but it doesn't feel right in comparison to the rest of the code. Is there a better way or is it the way to do it?

<div class="control-group@((!ViewData.ModelState.IsValidField("Password")) ? " error" : "")">