TextFinder tutorial: Designer "Go to Slot > clicked()" generates error

This from the TextFinder tutorial:

To call a find function when users press the Find button, you use the Qt signals and slots mechanism. A signal is emitted when a particular event occurs and a slot is a function that is called in response to a particular signal. Qt widgets have predefined signals and slots that you can use directly from Qt Designer. To add a slot for the find function:
Right-click the Find button to open a context-menu.
Select Go to Slot > clicked(), and then select OK.
A private slot, on_findButton_clicked(), is added to the header file, textfinder.h and a private function, TextFinder::on_findButton_clicked(), is added to the source file, textfinder.cpp.

However when I click on OK I get an error, no file matching ui_textfinder.h could be found.

Got around it by manually adding the necessary line in textfinder.h