diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 7cc9635..4eb6e55 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -10,8 +10,15 @@ sphinx:
   configuration: docs/conf.py
   fail_on_warning: true
 
+# Set the version of python needed to build these docs.
+build:
+  os: "ubuntu-22.04"
+  tools:
+    python: "3.8"
+  apt_packages:
+    - graphviz
+
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: "3.8"
   install:
   - requirements: requirements/docs.txt