Matlab 7.5 (2007b) Calling superclass function in overloaded subclass

When I call

p = inputParser2;
addRequired(p, 'A');

in Matlab 7.5 (2007b), with

classdef inputParser2 < inputParser
  methods
    function addRequired(obj, argname, varargin)
      addRequired@inputParser(obj, argname);
    end
  end
end

I get the error message

??? Error using ==> mcos_parent_function_
addRequired is not a method of base class inputParser.

Error in ==> inputParser2>inputParser2.addRequired at 5
      addRequired@inputParser(obj, argname);

But addRequired is clearly a method of class inputParser?