diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index a2e3f95..6c1bada 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -1,6 +1,7 @@
 version: 2
 
 python:
+  version: 3.9
   install:
   - requirements: requirements.txt
   - requirements: requirements-dev.txt