diff --git a/package.json b/package.json
index fb557305..033b4f32 100644
--- a/package.json
+++ b/package.json
@@ -89,7 +89,7 @@
     "mocha": "^11.0.0",
     "prettier": "3.8.1",
     "tailwind-csstree": "^0.2.0",
-    "typescript": "^5.9.3",
+    "typescript": "^6.0.2",
     "web-features": "^3.21.0",
     "yorkie": "^2.0.0"
   },
diff --git a/tests/types/tsconfig.json b/tests/types/tsconfig.json
index 4d6f9c30..106d8211 100644
--- a/tests/types/tsconfig.json
+++ b/tests/types/tsconfig.json
@@ -4,6 +4,8 @@
     "noEmit": true,
     "rootDir": "../..",
     "strict": true,
+    "strictNullChecks": true,
+    "useUnknownInCatchVariables": true,
     "exactOptionalPropertyTypes": true
   },
   "files": [],
diff --git a/tsconfig.json b/tsconfig.json
index 25070aa8..e33bc51a 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -10,6 +10,9 @@
     "lib": ["ES2022"],
     "moduleResolution": "NodeNext",
     "module": "NodeNext",
+    "rootDir": "./src",
+    "strictNullChecks": false,
+    "useUnknownInCatchVariables": false,
     "types": []
   }
 }