PHP fails at uniform distribution

rand.php

<?php

const RAND_MULTIPLE = 4;

$histogram = array_fill(0, getrandmax() * RAND_MULTIPLE, 0);

for ($i = 0; $i < 10000000; ++$i)
{
  $rnd = rand(0, getrandmax() * RAND_MULTIPLE);
  ++$histogram[$rnd];
}

for ($i = 0; $i < count($histogram); ++$i)
  echo "$i, $histogram[$i]\n";

?>