diff --git a/doc/requirements.txt b/doc/requirements.txt
index cffdd7bb..814ec044 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -2,5 +2,5 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 openstackdocstheme>=2.2.1 # Apache-2.0
-doc8>=0.6.0 # Apache-2.0
-sphinx>=2.0.0,!=2.1.0 # BSD
+doc8>=0.8.1 # Apache-2.0
+sphinx>=3.5.1 # BSD
diff --git a/tox.ini b/tox.ini
index 4f968ea5..070cdc41 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,12 +1,15 @@
 [tox]
-minversion = 2.0
+minversion = 4.0
 skipsdist = True
 envlist = docs
 
 [testenv]
 basepython = python3
 setenv = VIRTUAL_ENV={envdir}
-passenv = *_proxy *_PROXY ZUUL_*
+passenv =
+    *_proxy
+    *_PROXY
+    ZUUL_*
 
 [testenv:docs]
 setenv =