diff --git a/tox.ini b/tox.ini
index b4b54bc..af7d070 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,35 +1,35 @@
 [tox]
 envlist=flake8,py3,mypy
 
 [testenv]
 extras =
   testing
 deps =
   pytest-cov
   dev: pdbpp
 commands =
   pytest --cov={envsitepackagesdir}/swh/objstorage \
          {envsitepackagesdir}/swh/objstorage \
          --cov-branch {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
 deps =
   mypy
 commands =
   mypy swh