diff --git a/package-lock.json b/package-lock.json
index 0b1e6bdd..e6365d76 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -664,9 +664,9 @@
       "integrity": "sha1-3wEKoSh+Fku9pvlyOwqWoexBh6E="
     },
     "array-flatten": {
-      "version": "2.1.2",
-      "resolved": "https://registry.npmjs.org/array-flatten/-/array-flatten-2.1.2.tgz",
-      "integrity": "sha512-hNfzcOV8W4NdualtqBFPyVO+54DSJuZGY9qT4pRroB6S9e3iiido2ISIC5h9R2sPJ8H3FHCIiEnsv1lPXO3KtQ==",
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/array-flatten/-/array-flatten-3.0.0.tgz",
+      "integrity": "sha512-zPMVc3ZYlGLNk4mpK1NzP2wg0ml9t7fUgDsayR5Y5rSzxQilzR9FGu/EH2jQOcKSAeAfWeylyW8juy3OkWRvNA==",
       "dev": true
     },
     "array-from": {
@@ -988,6 +988,14 @@
         "dns-txt": "^2.0.2",
         "multicast-dns": "^6.0.1",
         "multicast-dns-service-types": "^1.1.0"
+      },
+      "dependencies": {
+        "array-flatten": {
+          "version": "2.1.2",
+          "resolved": "https://registry.npmjs.org/array-flatten/-/array-flatten-2.1.2.tgz",
+          "integrity": "sha512-hNfzcOV8W4NdualtqBFPyVO+54DSJuZGY9qT4pRroB6S9e3iiido2ISIC5h9R2sPJ8H3FHCIiEnsv1lPXO3KtQ==",
+          "dev": true
+        }
       }
     },
     "brace-expansion": {
diff --git a/package.json b/package.json
index ab4d78ea..e7549cc9 100644
--- a/package.json
+++ b/package.json
@@ -43,7 +43,7 @@
   },
   "devDependencies": {
     "@cybozu/eslint-config": "^8.0.0",
-    "array-flatten": "^2.1.2",
+    "array-flatten": "^3.0.0",
     "cssnano-cli": "^1.0.5",
     "eslint": "^6.6.0",
     "execa": "^2.1.0",