diff --git a/readthedocs.yml b/readthedocs.yml
index 72526f538..5f057c9ae 100644
--- a/readthedocs.yml
+++ b/readthedocs.yml
@@ -7,6 +7,8 @@ build:
   os: ubuntu-20.04
   tools:
     python: "3.10"
+  apt_packages:
+    - graphviz
   jobs:
     # build the gallery of themes before building the doc
     post_install: