I'm not getting any effect out of DOM.setElementAttribute, am I doing something wrong?

class MyListBox extends com.google.gwt.user.client.ui.ListBox {
  ....
  protected void setHoverAutoWidth() {
    addDomHandler(new MouseOverHandler() {
      public void onMouseOver(MouseOverEvent event) {
        DOM.setElementAttribute(getElement(), "width", "auto");
      }
    }, MouseOverEvent.getType());
    addDomHandler(new BlurHandler(){
      public void onBlur(BlurEvent event) {
        DOM.setElementAttribute(getElement(), "width", "100px");
      }
    }, BlurEvent.getType());
  }
}

(I know there are less hacky ways to change the width than to set the style attribute directly, but I don't care about css right now.)

Edit: Oops, just realized that width does not change the style width, just adds a width attribute to the tag (which explains why nothing happens). Any suggestions on how to modify the style are still welcome!