[Lazarus] where do I put project wide conditional define?

[Dennis]

I some of my units, I have :

uses classes,
{$IFDEF  USE_XYZ}
    certain_unitXYZ
{$ENDIF};


Where do I put
{$DEFINE USE_XYZ}

so that when I rebuild the project, fpc will see USE_XYZ is defined.

Putting in in the project .lpr  does not work

Thanks in advance.

Dennis

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