user.module line 528, warning: array_keys() [function.array-keys]: The first argument should be an array

I don't see anything obviously wrong with this code. All I can think of is that the $account variable has not been used prior to this statement but I'm not sure how to work around this so it stops yelling at me?

if (!isset($perm[$account->uid])) {
$result = db_query("SELECT p.perm FROM {role} r INNER JOIN {permission} p ON p.rid = r.rid WHERE r.rid IN ('. db_placeholders($account->roles) .')", array_keys($account->roles));

$perms = array();
while ($row = db_fetch_object($result)) {
$perms += array_flip(explode(', ', $row->perm));
}
$perm[$account->uid] = $perms;
}