How to debug from Fortran to C++

Hi, I have 2 projects in visual studio 15, one c++ and one fortran.

The Fortran project is using the c++ dll as a dynamic dll. It works just fine.

But I cannot debug from the Fortran code into the c++ code.

When I try to step from Fortran to the C++ code the debugger in VS takes me to a "Source not Available" page.

How to I setup my solution to I can debug from Fortran and into the c++ code?

Regards Torben