diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 223e768e843486cb41e2c23d66f79beba0981f89..132dc1c419e82fa585f1ae7d0e7f1438c3edf6db 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -7,6 +7,8 @@ version: 2
 
 build:
   os: ubuntu-20.04
+  tools:
+  - sphinx
 
 #conda:
 #  environment: envINEED_win.yml