How to use -isystem for include path instead of -I?

[Adeel Asghar]

If I use INCLUDEPATH in .pro file then qmake is using -I during the compilation but I want to use -isystem since I don't want to get the warning messages from those headers. How can I achieve this with qmake?

[Christian Ehrlicher]

Add your path also to QMAKE_DEFAULT_INCDIRS should work.

[Adeel Asghar]

Thanks but that doesn't work.
Following worked,

QMAKE_CXXFLAGS += -isystem includepath