diff --git a/.readthedocs.yml b/.readthedocs.yml
index bbfbc02..27a6134 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -1,4 +1,8 @@
 version: 2
+
+build:
+  tools:
+    python: "3.9"
 sphinx:
   configuration: conf.py
 python: