Enforce types SWIG

So I have the following C++

#include <stdio.h>
#include <iostream>
#include <vector>
using namespace std;

int hello(char *str);

int hello(char *str) {
    cout << "Hello World: " << str << endl;
    return 0;
}

And the following swig interface

%module sphp

%{
extern int hello(char *str);
%}

extern int hello(char *str);

And I can compile and use this in php,

php> hello("testing!");

This all is wicked!

Only problem is

php> hello(3);

is still valid. I don't want this, it seems swig silently casts types

  /*@SWIG:/usr/share/swig2.0/php/utils.i,62,CONVERT_STRING_IN@*/
  if ((*args[0])->type==IS_NULL) {
    arg1 = (char *) 0;
  } else {
    convert_to_string_ex(args[0]);
    arg1 = (char *) Z_STRVAL_PP(args[0]);
  }
  /*@SWIG@*/;

Now I don't want to be editing the wrapper, because its auto generated. Is there a way I can turn off this silent conversion, so that hello(3) will throw exceptions or errors, or can I give hello a hint about the type of the php argument it was originally passed?