diff --git a/doc/requirements.txt b/doc/requirements.txt
index af19231..0cb6f78 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,3 +1,4 @@
+sphinx==7.2.6 # verify that builds complete with this version
 matplotlib
 numpydoc
 sphinx-math-dollar