diff --git a/tox.ini b/tox.ini
index a35eedd..0ca2886 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,38 +1,38 @@
 [tox]
 envlist=black,flake8,mypy,py3
 
 [testenv]
 extras =
   testing
 deps =
   pytest-cov
 whitelist_externals =
   mvn
   sh
 commands =
   sh -c 'if ! [ -d {envdir}/share/swh-graph ]; then mvn -f java/pom.xml compile assembly:single; mkdir {envdir}/share/swh-graph; cp java/target/*.jar {envdir}/share/swh-graph; fi'
   pytest --cov={envsitepackagesdir}/swh/graph \
          {envsitepackagesdir}/swh/graph \
          --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