Lupdate can't find header file (Qualifying with unknown namespace/class)

Lupdate.exe can't find appropriate header for cpp file. As a result I am getting warning Qualifying with unknown namespace/class. That leads to wrong contexts in .ts files and unused translations in application.

I am using usual cmake folder structure like this one:

and source.cpp has such include:
#include "Target/header.h"

I am having warning when I call lupdate like this:

lupdate -target-language de_DE D:\Target\include\Target\header.h D:\Target\src\source.cpp -ts D:\separate_files.ts

D:/Target/src/source.cpp:8: Qualifying with unknown namespace/class ::Example

Meanwhile it is working as expected when I call lupdate with folder as argument:

lupdate -target-language de_DE D:\Target\ -ts D:\directory.ts