ghc -M: module `Main' is defined in multiple files

With ghc 6.4, ghc -M doesn't let me give multiple Main modules:

$ echo "module Main where main = return ()" > A.hs
$ echo "module Main where main = return ()" > B.hs
$ ghc -M A.hs B.hs
module `Main' is defined in multiple files: A.hs B.hs

This worked in 6.2.2.

In neither case are any dependencies mentioning Main generated, so I
don't think that this restriction is necessary.

This is annoying for a couple of reasons: it means I have to list all
the executables in my Makefile twice (once for the rules, once for a
"include .depend.Foo"), and it means that each change to a shared module
has to regenerate the dependency files for all executables, which takes
noticably longer.


Thanks
Ian