diff --git a/pyproject.toml b/pyproject.toml
index e209bdf..7c32764 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,7 +28,7 @@ dependencies = [
 dev = [
   "build>=1.2.2,<1.4.0",
   "ruff>=0.12.2,<0.15.0",
-  "sphinx>=7.3.7,<8.2.0",
+  "sphinx>=7.3.7,<9.2.0",
   "scikit-learn>=1.5,<1.8",
   "pre-commit>=4.0.1,<4.6.0"
 ]
@@ -45,7 +45,7 @@ homepage = "https://github.com/CyberAgentAILab/python-dte-adjustment"
 dev-dependencies = [
   "build>=1.2.2,<1.4.0",
   "ruff>=0.12.2,<0.15.0",
-  "sphinx>=7.3.7,<8.2.0",
+  "sphinx>=7.3.7,<9.2.0",
   "scikit-learn>=1.5,<1.8",
   "pre-commit>=4.0.1,<4.6.0"
 ]