diff --git a/CHANGES.rst b/CHANGES.rst
index 01a6623c..32897a01 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,6 +5,7 @@ CHANGES
 
 Unreleased
 ----------
+- Dependencies: Permitted installation of Sphinx 9.x
 
 2025/12/17 0.44.0
 -----------------
diff --git a/docs/build.json b/docs/build.json
index beb02da9..3e78651c 100644
--- a/docs/build.json
+++ b/docs/build.json
@@ -1,5 +1,5 @@
 {
   "schemaVersion": 1,
   "label": "docs build",
-  "message": "2.1.5"
+  "message": "sphinx9"
 }
diff --git a/setup.py b/setup.py
index ec773890..d7cd918e 100644
--- a/setup.py
+++ b/setup.py
@@ -65,7 +65,7 @@
         "myst-nb<1.4",
         "myst-parser[linkify]<5",
         "snowballstemmer<4",
-        "sphinx>=7.1,<9",
+        "sphinx>=7.1,<10",
         "sphinx-basic-ng==1.0.0b2",
         "sphinx-copybutton>=0.3.1,<1",
         "sphinx-design-elements==0.4.1",