S Function error: source file is included more than once

Hello Everyone,

I have build two S-Functions and each of them includes an external file (Custom.c, Custom.h). If I build code for an target hardware with including one of this S-Functions, then everything works just fine. But if both S-Functions are included, then it throws errors which say something like "multiple definition of functions inside Custom.c". I think there should be some technique to handle such situations? Thank you in advance! Best regards, GoldenEyes