This is not difficult to do and usually only requires adding a tag to your project file (example), but you need to make sure all the sources get into the package with the proper directory structure. Also, take into account Fable will just make a simple XML parsing to extract the source files from the .fsproj, so you should avoid MSBuild conditionals, etc. Because Fable will compile your sources you must be careful with compiler directives too (like #if MY_SYMBOL, etc). Though you can use this to your advantage and do some logging in debug mode (#if DEBUG). And remember also that Fable will always define the FABLE_COMPILER symbol when compiling to JS.