diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 6ee59775d9b87a37aa62dcf5410416e1b83ba08a..223e768e843486cb41e2c23d66f79beba0981f89 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -5,6 +5,9 @@
 # Required
 version: 2
 
+build:
+  os: ubuntu-20.04
+
 #conda:
 #  environment: envINEED_win.yml