Project ERROR: Unknown module(s) in QT: designer (QT Creator 3.5.1, QT 5.5.1, Linux Mint)

[Antinarella]

Hello everyone,
I'm new with QT. I'm trying to compile in Linux Mint an application previously written for Windows. I get the error

QtUiPlugin/QDesignerCustomWidgetInterface: No such file or directory
 #include <QtUiPlugin/QDesignerCustomWidgetInterface>
                                                     ^

Then I added to my project file the row

QT += designer

and I get

Project ERROR: Unknown module(s) in QT: designer

I installed both QT and QT creator via the official ubuntu repositories, and I made sure of installing libqt5designer5 and libqt5designercomponents5, but I can't get to a solution.
Does anybody have some suggestions? Thanks.

[Antinarella]

I solved just by installing the qttools via

sudo apt-get install qttools5-*

[Caio Fattori]

Problably, it was missing qttools5-dev.

I had this problem also, even with qttools5-designer5 installed.