Required_if laravel with multiple value

I have a dropdown menu like this:

<select name="selection">
   <option value="1">Option 1</option>
   <option value="2">Option 2</option>
   <option value="3">Option 3</option>
</select>
<input type="text" name="stext">

I want the following in laravel:

public static myfunction(){
   $input = Input::only('selection','stext');
   $rule = array(
      'selection' => 'required',
      'stext' => 'required_if:selection,2,3',
   );
   $validate = Validator::make($input,$rule);
}

But if I select option 1, stext is still required. Why? How can I fix it?

Answer

EDIT: As pointed out by LePhleg answer, there is a nicest syntax for this validation:

$rule = array(
  'selection' => 'required',
  'stext' => 'required_if:selection,2,3,
);

Old answer below:

I think that the require_if validation accept only one value per time. Try to change your validation code as below:

$rule = array(
  'selection' => 'required',
  'stext' => 'required_if:selection,2|required_if:selection,3',
);

EDIT: Check LePhleg answer, is more cleaner. At the time of the answer that was not possible, just check the question, he was using the same method but not worked.