diff --git a/.readthedocs.yml b/.readthedocs.yml
index d128268..518d481 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -15,6 +15,8 @@ build:
       - poetry config virtualenvs.create false
     post_install:
       - poetry install
+  apt_packages:
+    - graphviz
 
 sphinx:
   configuration: src/conf.py