Matlab Function Driver: Undefined reference to wrapper function

hey guys, i am using the matlab function block approach to implement a driver for external hardware on the raspi. As written in matlab's driver guide, i use the matlab function block to call two functions, say init_func() and output_func(). The latter functions are wrapper functions that enclose the actual c code which should be compiled and downloaded to the raspi. The c-code (with the wrapper functions) lies in an external c-file. As said in the guide, I added this C-file as a custom source with the set_param command. I also wrote an extra h-file which declares my wrapper functions. I included this h-file in my c-file. I also added this h-file as a custom source with the set_param command. When I build the model, Matlab gets so far that it generates the c-File for the simulink block but it errors: MySimulinkBlock.c:(.text+0x1c): undefined reference to `init_func' MySimulinkBlock.c:(.text+0x2f8): undefined reference to `output_func'

This means that my wrapper functions are somehow not found. Any ideas? Thanks!