PyPy + Cpython extension written with Rust (rust-cpython)

I was going to try using PyPy. But an extension (.so file) I wrote with rust-cpython can't be loaded when executed with pypy3:

ImportError: No module named 'pkg.lib'

where lib is my lib.so file.

CPython(3.5) loads it fine. I thought PyPy had support for loading CPython extensions.

If not - what do I need to do to load .so file compiled with Rust (rust-cpython)?