diff --git a/pyproject.toml b/pyproject.toml
index bfd1761..67ef135 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,7 +28,7 @@ dependencies = [
 dev = [
   "build~=1.2.2",
   "ruff~=0.12.2",
-  "sphinx~=7.3.7",
+  "sphinx>=7.3.7,<8.2.0",
   "scikit-learn~=1.5.0",
   "pre-commit~=4.0.1"
 ]
@@ -45,7 +45,7 @@ homepage = "https://github.com/CyberAgentAILab/python-dte-adjustment"
 dev-dependencies = [
   "build~=1.2.2",
   "ruff~=0.12.2",
-  "sphinx~=7.3.7",
+  "sphinx>=7.3.7,<8.2.0",
   "scikit-learn~=1.5.0",
   "pre-commit~=4.0.1"
 ]