diff --git a/requirements.txt b/requirements.txt
index 4d6b2210c..61bfa46ee 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,7 +10,7 @@ pytest-cov>=2.6.0
 
 flake8>=3.5.0
 
-sphinx<8.2.0
+sphinx<9.1.0
 sphinx_book_theme
 sphinxcontrib-bibtex
 sphinx-math-dollar