diff --git a/h2o-docs-theme/package.json b/h2o-docs-theme/package.json
index d5bbf203dadb..8fdb99657114 100644
--- a/h2o-docs-theme/package.json
+++ b/h2o-docs-theme/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "dependencies": {},
   "devDependencies": {
-    "grunt": "~0.4.1",
+    "grunt": "~1.6.1",
     "grunt-contrib-sass": "~0.7.2",
     "grunt-contrib-watch": "~0.4.3",
     "grunt-contrib-connect": "0.5.0",