rustpkg can't find std on Windows

[jhasse]

I've installed latest rust on Windows built with MinGW GCC 4.7.0. I've tried installing with prefix /mingw and /usr/local. Both times I'm getting the following error when using rustpkg (no matter which package):

$ rustpkg build sdl2
WARNING: The Rust package manager is experimental and may be unstable
error: Package sdl2 depends on std, but I don't know how to find it
task '<unnamed>' failed at 'explicit failure', C:\Users\jhass_000\git\rust\src\librustpkg\util.rs:502
task '<unnamed>' failed at 'receiving on closed channel', C:\Users\jhass_000\git\rust\src\libstd\rt\comm.rs:199

I've also tried

$ export RUST_PATH=/mingw/bin

because std-6425b930ca146ae9-0.9-pre.dll is there.