I needed to introduce this new ctor because I am using a KPlotWidget in a .ui file in Kalzium (see Revision 596474). The uic always uses Foo(QWidget*) and you cannot change this. Therefor I need a KPlotWidget(QWidget*)-ctor. Another solution would be to change the order of the arguements so that the QWidget = 0 would be at the first position. I would of course prefere that solution as it would remove this stupid second ctor.