diff --git a/package.json b/package.json
index b4d8bb7..a6e1e6f 100644
--- a/package.json
+++ b/package.json
@@ -50,7 +50,7 @@
     },
     "devDependencies": {
         "@eslint-community/eslint-plugin-mysticatea": "^15.5.1",
-        "c8": "^8.0.1",
+        "c8": "^9.1.0",
         "dot-prop": "^7.2.0",
         "eslint": "^8.50.0",
         "mocha": "^9.2.2",