Migration for creating missing indexes does not work with sqlite

$ alembic upgrade head
INFO [alembic.migration] Context impl SQLiteImpl.
INFO [alembic.migration] Will assume non-transactional DDL.
INFO [alembic.migration] Running upgrade None -> 5ef013efbc2, create tests tables
INFO [alembic.migration] Running upgrade 5ef013efbc2 -> 1f92cfe8a6d3, create runs table
INFO [alembic.migration] Running upgrade 1f92cfe8a6d3 -> 3db7b49816d5, create test_runs table
INFO [alembic.migration] Running upgrade 3db7b49816d5 -> 163fd5aa1380, Create avg runtime column in test table
INFO [alembic.migration] Running upgrade 163fd5aa1380 -> 4ca26dac400e, Create metadata tables
INFO [alembic.migration] Running upgrade 4ca26dac400e -> 13d819bbb0ff, create missing indexes
Traceback (most recent call last):
  File "/home/af/venvs/subunit2sql/bin/alembic", line 9, in <module>
    load_entry_point('alembic==0.6.5', 'console_scripts', 'alembic')()
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/config.py", line 298, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/config.py", line 293, in main
    self.run_cmd(cfg, options)
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/config.py", line 279, in run_cmd
    **dict((k, getattr(options, k)) for k in kwarg)
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/command.py", line 125, in upgrade
    script.run_env()
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/script.py", line 203, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/util.py", line 212, in load_python_file
    module = load_module_py(module_id, path)
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/compat.py", line 58, in load_module_py
    mod = imp.load_source(module_id, path, fp)
  File "subunit2sql/migrations/env.py", line 83, in <module>
    run_migrations_online()
  File "subunit2sql/migrations/env.py", line 76, in run_migrations_online
    context.run_migrations()
  File "<string>", line 7, in run_migrations
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/environment.py", line 688, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/migration.py", line 258, in run_migrations
    change(**kw)
  File "subunit2sql/migrations/versions/13d819bbb0ff_create_missing_indexes.py", line 35, in upgrade
    ['test_id', 'run_id'])
  File "<string>", line 7, in create_unique_constraint
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/operations.py", line 621, in create_unique_constraint
    schema=schema, **kw)
  File "/home/af/venvs/subunit2sql/local/lib/python2.7/site-packages/alembic/ddl/sqlite.py", line 21, in add_constraint
    "No support for ALTER of constraints in SQLite dialect")
NotImplementedError: No support for ALTER of constraints in SQLite dialect

Environment:

$ pip freeze | egrep '(subunit|oslo|alem)'
alembic==0.6.5
oslo.config==1.4.0.0a3
oslo.db==0.3.0
python-subunit==0.0.18
subunit2sql==0.2.dev4.g10e5d0e