Big trigger, small error 1064

[Frantisek Dobrota]

I really don't know where I made the mistake, I think code this should work:

DELIMITER |
CREATE TRIGGER `parOSOnInsert` BEFORE INSERT
ON `Partition_has_Operating_System` FOR EACH ROW
BEGIN
    IF ((NEW.`Operating_System_id_OS` IN SELECT `Operating_System_id_OS` FROM
        `CompanyPCs`.`Operating_System_has_Kernel` JOIN `CompanyPCs`.`Kernel` JOIN
        `CompanyPCs`.`Kernel_supports_Filesystem` JOIN `CompanyPCs`.`Filesystem` JOIN
        `CompanyPCs`.`Partition_has_Filesystem`
        WHERE `Operating_System_has_Kernel`.`Kernel_Kernel_Type` = `Kernel`.`Kernel_Type`
            AND `Operating_System_has_Kernel`.`Kernel_Kernel_version` = `Kernel`.`Kernel_version`
            AND `Filesystem`.`Filesystem_Name` = `Kernel_supports_Filesystem`.`Filesystem_Filesystem_Name`
            AND `Filesystem`.`Filesystem_Name` = `Partition_has_Filesystem`.`Filesystem_Filesystem_Name`
            AND `Partition_has_Filesystem`.`Partition_idPartition` = NEW.`Partition_idPartition`
            AND `Partition_has_Filesystem`.`Partition_HDD_idHDD` = NEW.`Partition_HDD_idHDD` 
            AND `Partition_has_Filesystem`.`Partition_HDD_PC_idPC` = NEW.`Partition_HDD_PC_idPC`
            AND `Partition_has_Filesystem`.`Partition_HDD_PC_roomNr` = NEW.`Partition_HDD_PC_roomNr`),
        SELECT 1 = 1,
        SIGNAL SQLSTATE 'F9F54'
            set MESSAGE_TEXT = 'Filesystem unsupported by OS Kernel');
END; |
DELIMITER ;

but it throw me ERROR 1064 (42000) near SELECT `Operating_System_id_OS` FROM
`CompanyPCs`.`Operating_System_has' at line 4
I know this solution might not be the best one, but I need to do something quickly.