diff --git a/.circleci/config.yml b/.circleci/config.yml
index 2da27550d..c60601bce 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -58,17 +58,17 @@ jobs:
       - run:
           name: Install dependencies
           command: npm install
+      - save_cache:
+          key: v2-npm-lock-{{ .Branch }}-{{ .Environment.CIRCLE_JOB }}-{{ checksum "package.json" }}
+          paths:
+            - node_modules
       - run:
           name: Install eslint 5
           command: |
             # We need to execute this command twice because of npm's bug.
             # See also: https://npm.community/t/error-node-modules-staging-eslint-e7cf6846-node-modules-eslint
-            npm install eslint@5.0.0 --no-save
-            npm install eslint@5.0.0 --no-save
+            npm install eslint@5.0.0 acorn@6.0.7 --no-save
+            npm install eslint@5.0.0 acorn@6.0.7 --no-save
       - run:
           name: Test
           command: npm test
-      - save_cache:
-          key: v2-npm-lock-{{ .Branch }}-{{ .Environment.CIRCLE_JOB }}-{{ checksum "package.json" }}
-          paths:
-            - node_modules
diff --git a/package.json b/package.json
index 3f6573ea6..8246a88b8 100755
--- a/package.json
+++ b/package.json
@@ -51,6 +51,7 @@
   "devDependencies": {
     "@types/node": "^4.2.16",
     "@typescript-eslint/parser": "^1.11.0",
+    "acorn": "^7.0.0",
     "babel-eslint": "^10.0.2",
     "chai": "^4.1.0",
     "eslint": "^6.0.0",