diff --git a/package-lock.json b/package-lock.json
index 60ee972e..8396f556 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1618,9 +1618,9 @@
       }
     },
     "acorn": {
-      "version": "6.1.1",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.1.1.tgz",
-      "integrity": "sha512-jPTiwtOxaHNaAPg/dmrJ/beuzLRnXtB0kQPQ8JpotKJgTB6rX6c8mlf315941pyjBSaPg8NHXS9fhP4u17DpGA==",
+      "version": "6.4.1",
+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.4.1.tgz",
+      "integrity": "sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==",
       "dev": true
     },
     "acorn-dynamic-import": {
diff --git a/package.json b/package.json
index 51e8c5e2..93a9337a 100644
--- a/package.json
+++ b/package.json
@@ -111,7 +111,7 @@
     "@hackmd/idle-js": "~1.0.1",
     "@hackmd/js-sequence-diagrams": "~0.0.1-alpha.3",
     "@susisu/mte-kernel": "^2.1.0",
-    "acorn": "~6.1.1",
+    "acorn": "~6.4.1",
     "babel-core": "~6.26.3",
     "babel-loader": "~7.1.4",
     "babel-plugin-transform-runtime": "~6.23.0",