diff --git a/swh/__init__.py b/swh/__init__.py
index 8d9f151..b36383a 100644
--- a/swh/__init__.py
+++ b/swh/__init__.py
@@ -1,4 +1,3 @@
 from pkgutil import extend_path
-from typing import List
 
-__path__: List[str] = extend_path(__path__, __name__)
+__path__ = extend_path(__path__, __name__)
diff --git a/tox.ini b/tox.ini
index 63a3a55..9126a08 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,94 +1,94 @@
 [tox]
 envlist=black,flake8,mypy,py3-{core,db,server}
 
 [testenv]
 passenv = PYTHONASYNCIODEBUG
 extras =
   testing-core
   core: logging
   db: db
   server: http
 deps =
   cover: pytest-cov
 commands =
   pytest --doctest-modules \
   slow: --hypothesis-profile=slow \
   cover: --cov={envsitepackagesdir}/swh/core --cov-branch \
   core: {envsitepackagesdir}/swh/core/tests \
   db: {envsitepackagesdir}/swh/core/db/tests \
   server: {envsitepackagesdir}/swh/core/api/tests \
     {posargs}
 
 [testenv:py3]
 skip_install = true
 deps = tox
 commands = tox -e py3-core-db-server-slow-cover -- {posargs}
 
 [testenv:black]
 skip_install = true
 deps =
   black==19.10b0
 commands =
   {envpython} -m black --check swh
 
 [testenv:flake8]
 skip_install = true
 deps =
   flake8
 commands =
   {envpython} -m flake8
 
 [testenv:mypy]
 extras =
   testing-core
   logging
   db
   http
 deps =
-  mypy
+  mypy==0.920
 commands =
   mypy swh
 
 # build documentation outside swh-environment using the current
 # git HEAD of swh-docs, is executed on CI for each diff to prevent
 # breaking doc build
 [testenv:sphinx]
 whitelist_externals = make
 usedevelop = true
 extras =
   testing-core
   logging
   db
   http
 deps =
   # fetch and install swh-docs in develop mode
   -e git+https://forge.softwareheritage.org/source/swh-docs#egg=swh.docs
 
 setenv =
   SWH_PACKAGE_DOC_TOX_BUILD = 1
   # turn warnings into errors
   SPHINXOPTS = -W
 commands =
   make -I ../.tox/sphinx/src/swh-docs/swh/ -C docs
 
 
 # build documentation only inside swh-environment using local state
 # of swh-docs package
 [testenv:sphinx-dev]
 whitelist_externals = make
 usedevelop = true
 extras =
   testing-core
   logging
   db
   http
 deps =
   # install swh-docs in develop mode
   -e ../swh-docs
 
 setenv =
   SWH_PACKAGE_DOC_TOX_BUILD = 1
   # turn warnings into errors
   SPHINXOPTS = -W
 commands =
   make -I ../.tox/sphinx-dev/src/swh-docs/swh/ -C docs