I am porting code from qt4 to qt5. I added the following line to my `.pro` file, [as suggested](http://qt-project.org/wiki/Transition_from_Qt_4.x_to_Qt5):

```
QT += webkitwidgets

```

However, when I run `qmake`, I get the this error:

```
Project ERROR: Unknown module(s) in QT: webkitwidgets

```

I am developing on Ubuntu 12.04 LTS and installed Qt [as described](https://askubuntu.com/questions/279421/how-can-i-install-qt-5-x-on-12-04-lts).