diff --git a/doc/conf.py b/doc/conf.py
index 1f5625acd3b4..d2228ccba0a0 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -36,7 +36,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ["sphinx.ext.todo", "sphinx.ext.graphviz", "sphinx.ext.autodoc"]
+extensions = ["sphinx.ext.todo", "sphinx.ext.graphviz", "sphinx.ext.autodoc", "sphinx_rtd_theme"]
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ["_templates"]
diff --git a/vm/ubuntu/topotato-install.sh b/vm/ubuntu/topotato-install.sh
index 2f5e5664dca2..523532712c1e 100644
--- a/vm/ubuntu/topotato-install.sh
+++ b/vm/ubuntu/topotato-install.sh
@@ -9,3 +9,7 @@ sudo DEBIAN_FRONTEND=noninteractive apt install graphviz tshark \
    python3-venv wireshark-common python3-pip tini -y
 
 pip install -r requirements.txt
+
+# sphinx documentation
+
+pip install sphinx_rtd_theme
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