diff --git a/.readthedocs.yml b/.readthedocs.yml
index d9f08a27..e8e6f458 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -4,6 +4,7 @@
 version: 2
 
 build:
+  os: ubuntu-20.04
   tools:
     python: "3.10"