GEANT3 compilation does not find headers

Dear experts,

when building GEANT3 v2-7 I get the following error message:

In file included from /Users/mkrueger/alice/sw/SOURCES/GEANT3/v2-7/v2-7/TGeant3/TG3Application.cxx:9:
/Users/mkrueger/alice/sw/SOURCES/GEANT3/v2-7/v2-7/TGeant3/TG3Application.h:12:10: fatal error: ‘TVirtualMCApplication.h’ file not found
#include <TVirtualMCApplication.h>
^~~~~~~~~~~~~~~~~~~~~~~~~
[ 99%] Building CXX object CMakeFiles/geant321.dir/TGeant3/TGeant3f77.cxx.o
In file included from /Users/mkrueger/alice/sw/SOURCES/GEANT3/v2-7/v2-7/TGeant3/TGeant3f77.cxx:25:
In file included from /Users/mkrueger/alice/sw/SOURCES/GEANT3/v2-7/v2-7/TGeant3/TGeant3f77.h:9:
/Users/mkrueger/alice/sw/SOURCES/GEANT3/v2-7/v2-7/TGeant3/TGeant3.h:21:10: fatal error: ‘TVirtualMC.h’ file not found
#include “TVirtualMC.h”

The full log can be found here: https://cernbox.cern.ch/index.php/s/stExHKxANkBsfl9

My system is Mac OS Catalina 10.15.3.
I would be happy about any hints or suggestions.

Cheers,
Mario

Looks like you are picking up a ROOT installation from the system:

-- Found ROOT 6.18/04 in /usr/local/Cellar/root/6.18.04_2
-- Configuring done
CMake Warning (dev):

This should not happen since ROOT should always be taken from the alidist software stack (right @ktf?).
Please check that you are not setting any environment variables that mislead alibuild.

P.S. Newer versions of ROOT could disable TVirtualMC which seems to be the case in your system ( homebrew ?? ) installation.

Hello Sandro,
indeed, I had sourced thisroot.sh of my brew installation in the .bashrc before starting aliBuild.
I assumed that that the aliBuild system would override the ROOT variables accordingly.
Anyway, thank you very much for your help!

Cheers,
Mario