diff --git a/.readthedocs.yml b/.readthedocs.yml
index 4400f9f..273c59e 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -9,7 +9,7 @@ version: 2
 build:
   os: ubuntu-22.04
   tools:
-    python: 3.9
+    python: "3.9"
 
 # Build documentation in the docs/ directory with Sphinx
 sphinx: