spinbox up/down buttons not hidding correctly

I'm using a spinbox of which I want to hide the up/down buttons. So I use this NoButtons symbol as follow :

 
distanceBox->setButtonSymbols(QAbstractSpinBox::NoButtons);

 
The buttons seems hidden, but their layout is still here. I mean the space they should occupy is still here. And so the text appear truncated even though the box is big enough. See my text on the picture which should be '116.96 mm'.

Expected behavior: the layout of the button is removed, so that the text can expand on the whole box.