diff --git a/doc/conf.py b/doc/conf.py
index 5da5561bf..ff42334bd 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -40,7 +40,8 @@ extensions = [
     'sphinx.ext.autodoc',
     'sphinx.ext.intersphinx',
     'sphinx.ext.viewcode',
-    'm2r',
+    'sphinxcontrib.plantuml',
+    'm2r2',
 ]
 
 # Add any paths that contain templates here, relative to this directory.
diff --git a/doc/requirements.txt b/doc/requirements.txt
index 8b96bc9bc..186d92c7b 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,8 +1,11 @@
-## m2r is not compatible with Sphinx 3.x yet
-sphinx >2.1,<3.0
+wheel
 
-## convert markdown to rest
-m2r
+sphinx
+
+# convert markdown to rest
+# m2r2 fork is active in development and works with
+# newer sphinx versions
+m2r2
 
 ## ipa dependencies
 dnspython
@@ -26,3 +29,7 @@ lxml
 
 ## No sufficient PyPI packages
 # dogtag-pki
+
+# Sequence diagrams generator
+sphinxcontrib-plantuml
+pillow