diff --git a/tox.ini b/tox.ini
index f87c7ee..4e0be5e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,52 +1,52 @@
 [tox]
 envlist=black,flake8,mypy,py3-{core,db,server}
 
 [testenv]
 extras =
   testing-core
   core: logging
   db: db, testing-db
   server: http
 deps =
   db: pifpaf
   cover: pytest-cov
 commands =
   db: pifpaf run postgresql -- \
     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
+  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
   testing-db
   http
 deps =
   mypy
 commands =
   mypy swh