Sorry to hijack CPython's bug tracker for that, but can you check if this makes sense to you?  I added a function 'locals_to_fast()' to the __pypy__ built-in module which just calls the PyPy equivalent to PyFrame_LocalsToFast().  Your tests are passing, so I guess there should be no problem.  The diff is here: http://bpaste.net/show/176119/ (are you ok with having your name put into the test file?).