diff --git a/package.json b/package.json
index e60192b..09a97e3 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,7 @@
   },
   "devDependencies": {
     "babel-cli": "^6.x",
-    "babel-core": "^6.x",
+    "babel-core": "^6.3.15",
     "babel-preset-es2015": "^6.x",
     "benchmark": "^1.x",
     "finalhandler": "^0.x",