diff --git a/doc/requirements.txt b/doc/requirements.txt
index c0d4f09..5d5cabe 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,4 +1,5 @@
-Sphinx>=4
+sphinx<7
+sphinx_rtd_theme
 matplotlib
 numpy
 numpydoc