diff --git a/.readthedocs.yml b/.readthedocs.yml
index 491111625..65337119d 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -1,5 +1,10 @@
 version: 2
 
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.9"
+
 sphinx:
   configuration: doc/conf.py
 
@@ -8,6 +13,5 @@ formats:
   - pdf
 
 python:
-  version: 3.6
   install:
     - requirements: doc/requirements.txt
diff --git a/doc/requirements.txt b/doc/requirements.txt
index ed4290d62..ba2692b40 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,5 +1,5 @@
 breathe
 recommonmark
-Sphinx>=2.0
+sphinx<7
 sphinx_rtd_theme
 sphinxcontrib-bibtex==1.0.0