my $fen = $cgi->param('fen');
my $pos = Position->from_fen($fen);
my $hex = unpack('H*', $pos->bitpacked_fen);
-open my $fh, "-|", "../binlookup", "../open.mtbl", $hex
+open my $fh, "-|", "../binlookup", "../open.mtbl", "40", $hex
or die "../binlookup: $!";
my $opening;