Use enum in h:selectManyCheckbox

I want to use enum values in a <h:selectManyCheckbox>. The checkboxes get populated correctly, however, when selecting some values and submitting them, their runtime type is String, and not enum. My code:

<h:selectManyCheckbox value="#{userController.roles}" layout="pageDirection">
     <f:selectItems value="#{userController.rolesSelectMany}" />
</h:selectManyCheckbox>

UserController class (SecurityRole is an enum type):

public SelectItem[] getRolesSelectMany() {
    SelectItem[] items = new SelectItem[SecurityRole.values().length];

    int i = 0;
    for (SecurityRole role : SecurityRole.values()) {
        items[i++] = new SelectItem(role, role.toString());
    }
    return items;
}     

public List<SecurityRole> getRoles() {
     getCurrent().getRoles();
}

public void setRoles(List<SecurityRole> roles) {
     getCurrent().setRoles(roles);
}

When JSF calls the setRoles method, it contains a list of type String, and not the enum type. Any ideas? Thanks!