diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 544d704c..75eabe26 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -1,4 +1,10 @@
 version: 2
+
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.9"
+
 python:
   install:
     - method: pip