mysterious directory include error

Here is my program:

#!/usr/bin/runghc -i./foo
main :: IO ()
main = do
    print "hi"

$ runghc --version
The Glorious Glasgow Haskell Compilation System, version 6.4
$ ls foo          
$ ./test.hs

<interactive>:1:85:
    Failed to load interface for `Main':
        Could not find module `Main':
          it is not a module in the current program, or in any known package.

Let me know if any more information is needed!

Frederik

-- 
http://ofb.net/~frederik/