We currently patch qtchooser to make it look for configs in three additional directories: - /usr/share/qtchooser: holds qtx-triplet.conf configs. They are installed by libqtcore with it's arch triplet. In this way apps can call it's specific arch tools. - /usr/lib/$(DEB_HOST_MULTIARCH)/qtchooser: holds qtx.conf and default.conf for the specific arch. - /usr/lib/$(DEB_HOST_MULTIARCH)/qt-default/qtchooser: holds a default.conf which points to Qt4. In this way the Qt4 packages already in the archive should not FTBFS when we introduce qtchooser in unstable. Exporting QT_SELECT=qt4 or build-depending on qt4-default is recommended. = Bootstrapping qtchooser. qtchooser build-depends on qtbase5-dev, but qtchooser itself is needed in order to run qmake, so creating a circular build dependency. Actually qtchooser only needs Qt5 for building its tests. If you need to bootstrap it, build it with either stage1 or nocheck build profile.