Compiling error with qtractor

Dear Rui!
When compiling qtractor's latest code I get the following error:
==================================
In file included from qtractorTrackList.cpp:23:0:
qtractorTrackList.h:286:33: error: field ‘m_tracks’ has incomplete type ‘QHash’
QHash m_tracks;
^
In file included from /usr/include/qt4/QtGui/qwidget.h:46:0,
from /usr/include/qt4/QtGui/qframe.h:45,
from /usr/include/qt4/QtGui/qabstractscrollarea.h:45,
from /usr/include/qt4/QtGui/QAbstractScrollArea:1,
from qtractorScrollView.h:25,
from qtractorTrackList.h:25,
from qtractorTrackList.cpp:23:
/usr/include/qt4/QtGui/qwindowdefs.h:148:34: note: declaration of ‘class QHash’
template class QHash;
^
In file included from qtractorTrackList.cpp:23:0:
qtractorTrackList.h:289:21: error: field ‘m_select’ has incomplete type ‘QHash’
QHash m_select;
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If it is a qt4 issue I am fine with it anyway.
Thanks and greetings, Michael