diff --git a/tox.ini b/tox.ini
index 0d65b024fc5..95e5db64d8a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -141,6 +141,9 @@ envdir = {toxworkdir}/docs
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
+# NOTE(slaweq): mitogen is optional dependency of the pyroute2 and without it
+# our docs job is failing
+  mitogen>=0.2.9
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:pdf-docs]