stack build works as expected but stack runghc can't find local modules

So I have a Haskell project (managed using stack) structured like this:

.
├── Main.hs
├── Other1.hs
├── subfolder
    └── Other2.hs

where the Main module imports both Other1 and Other2, as simply as

import Other1
import Other2

My .cabal file says:

name: (...)

executable Main
hs-source-dirs:
  .,
  subfolder
main-is: Main.hs
other-modules:
  Other1
  Other2

Now, if I run stack build everything works great, all modules are compiled and it looks like nothing can go wrong. But then if I try to execute my program with stack runghc Main, module Other2 (the one in the subfolder) is not found.

Why is that the case? How can I execute my code?