Unknown module(s) in QT: webkitwidgets

[Bull]

I am new with qt5 and have installed from scratch using this tutorial here: http://www.linuxfromscratch.org/blfs/view/svn/x/qt5.html

Qt5 is installed in /opt/qt5/qt-5.4.1.

I have also done sudo apt-get install libqt5webkit5-dev.

However, when I tried to include webkitwidgets in my .pro file, the error is returned: Unknown module(s) in QT: webkitwidgets

Here is a snippet of my .pro:

QT += core gui

QT += widgets webkitwidgets

INCLUDEPATH += /opt/lib/eigen-eigen-10219c95fe65
/opt/qt5/qt-5.4.1/lib

What am I missing here?

Thanks.