The compiler crashes at Emit step because the return has not been inferred and thus unknown. http://monoport.com/6530 {{ import System.Runtime.InteropServices class Test: def constructor(): #exit(1) uncomment this line and it will work pass [DllImport("libc")] #comment this line and it will work private static def exit(status as int): #adding as void would make it work too pass Test() }}