diff --git a/readthedocs.yaml b/readthedocs.yaml
index c3ab4aa..7643348 100644
--- a/readthedocs.yaml
+++ b/readthedocs.yaml
@@ -1,8 +1,11 @@
 version: 2
 
+build:
+  os: ubuntu-20.04
+
 sphinx:
   configuration: docs/conf.py
-
+  
 formats:
   - "htmlzip"
   - "pdf"