diff --git a/.readthedocs.yml b/.readthedocs.yml
index 8ebaf5e..dcaaaba 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -18,6 +18,8 @@ python:
   install:
     - method: pip
       path: .
+      extra_requirements:
+        - rtd
 
 # Don't build any extra formats
 formats: []
diff --git a/setup.cfg b/setup.cfg
index b2013c0..5d7a16b 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -20,7 +20,7 @@ zip_safe = False
 packages = find:
 python_requires = >=3.7
 install_requires =
-    sphinx>=2
+    sphinx>=4
 
 [options.extras_require]
 test =
@@ -28,6 +28,10 @@ test =
     pytest-cov
     cython
     coverage
+rtd =
+    # https://github.com/readthedocs/sphinx_rtd_theme/issues/1463
+    sphinx<7
+    sphinx-rtd-theme
 
 [options.package_data]
 sphinx_automodapi = templates/*/*.rst