simulink.h missing in 2019a

I am trying to build a simulink file in Matlab 2019a. The build is successful in 2018b.

But in 2019a I get the error:

Error using mex
grampc_run_Sfct.c
C:\[...]\matlab\bin\grampc_run_Sfct.c(32): fatal error C1083: Cannot open
include file: 'simstruc.h': No such file or directory

What is the issue?

Using Visual Studio 2017:

MEX configured to use 'Microsoft Visual C++ 2017 (C)' for C language compilation.