CLONE - dash in script filename

Cannot create script with dash ("-") in filename.

Please try to run the two attached groovy scripts. The one with an underscore in the filename runs happily (don't wonder, it gives no output). The one with a dash in the filename gives this error:

$ groovy fibonacci-numbers.groovy
Caught: java.lang.ClassFormatError: Illegal class name "fibonacci-numbers$fib" in class file fibonacci-numbers$fib
java.lang.ClassFormatError: Illegal class name "fibonacci-numbers$fib" in class file fibonacci-numbers$fib
        at fibonacci-numbers.run(fibonacci-numbers.groovy:5)

It really took me some time to figure out that the dash was causing this. I would like to see Groovy allowing dashes in script filenames. If that should be impossible, at least the error message should cleary indicate that I have used an illegal character in the script filename.