>>> foo = 'oops' >>> from . import foo as fubar # should raise ImportError >>> fubar 'oops' After further investigation, the problem is that builtins.__import__ (the c port version) does not replicate the behaviour of importlib.__import__ (the python reference version): >>> import builtins, importlib >>> __package__ is None True >>> importlib.__import__('', globals(), locals(), ('foo',), 1) ImportError >>> builtins.__import__('', globals(), locals(), ('foo',), 1) <module '__main__' (built-in)> A further discrepancy is that for deeper relative imports, builtins.__import__ raises a ValueError instead of ImportError (contrary to expectation/spec): >>> from ...... import foo ValueError A simple work around uses the python implementation to restore expected behaviour: >>> builtins.__import__ = importlib.__import__ >>> from ...... import foo ImportError >>> from curses import ascii >>> from . import ascii ImportError PS: Brett Cannon, to replicate please copy and paste lines in correct order :-)