php - syntax error, unexpected T_IS_EQUAL

            if(isset($_POST['zapisz'])) { 
    $zapytanie_update = mysql_query("UPDATE `emotki` SET `kod` = '".$_POST['kod']."',`opis` = '".$_POST['opis']."', `glowna` = '".$_POST['glowna']."' WHERE id= $id");
    echo 'Emotka zapisana.
« Powrót';
    }


    $usun = $_POST['usun'];
    if(isset($usun == 1)
    {
    $usuwaj = mysql_query("DELETE FROM `emotki` WHERE 'id'= $id");
    }



else {
?>

i have
( ! ) Parse error: syntax error, unexpected T_IS_EQUAL, expecting ',' or ')' in C:\wamp\www\emotki_admin\edytuj.php on line 63

line 63 is if(isset($usun == 1)

where is error?