How to access undefined unreal class

Hi, i can’t seem to access the UTextRenderComponent class of UE4 for the timer tutorial, it appears to be undefined so i can’t use its functions. Is this a bug or am I doing something wrong?
A screenshot: http://puu.sh/jeTTE/90fc84993c.png

You will need to add

#include "Engine.h"

to your header file Countdown.h. Make sure it is not the last include statement, though.