Cannot import gi.repository.* on Python 3.6.5

On Mac/Homebrew:

$ python3 -c "from gi.repository import Gst"                
Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 888, in _find_spec
AttributeError: 'DynamicImporter' object has no attribute 'find_spec'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python3.6/site-packages/gi/importer.py", line 128, in find_module
    'introspection typelib not found' % namespace)
ImportError: cannot import name Gst, introspection typelib not found


$ ls /usr/local/lib/python3.6/site-packages/gi/overrides 
GIMarshallingTests.py		Gdk.py				GstPbutils.py			__init__.py			keysyms.py
GLib.py				Gio.py				Gtk.py				__pycache__
GObject.py			Gst.py				Pango.py			_gi_gst.cpython-36m-darwin.so


$ python3 --version
Python 3.6.5