Declaration should be compatible with Base

DeclarationShouldBeCompatibleWithBase.php

<?php

class ModelA{
    public function sayHi() { return "hi"; }
}
class ModelB extends ModelA {
    public function sayHi() { return "hello"; }
}

class SomethingA{
    public function doStuff(ModelA $model) {
        echo $model->sayHi();
    }
}
class SomethingB extends SomethingA{
    public function doStuff(ModelB $model) {
        echo $model->sayHi();
    }
}

$something = new SomethingB();
$something->doStuff(new ModelB());

/**
( ! ) Strict standards: Declaration of SomethingB::doStuff() should be compatible with SomethingA::doStuff(ModelA $model) in file.php on line 19