Compile .kt files nested in folders with kotlinc

Question

I want to use kotlinc to compile multiple files that are organized in folders, like in this minimal example:

Main.kt only calls helper.kt which contains

When I call: kotlinc *.kt -include-runtime -d Main.jar

I get the error

I guess the problem is that *.kt doesn't compile files nested in folders. How do I change that? I didn't find a flag for it in the kotlinc documentation.