qmake run command only in debug mode, how?

This is kind of a continuation of this question. I want to run

win32:LIBS ~= s/-l(.*)/-l\1d/g

only for debug builds, since the idea is to appen d to lib names in debug mode.

I tried

win32:debug:LIBS ~= s/-l(.*)/-l\1d/g

But so it also executes in release mode.