diff --git a/app.json b/app.json
index 3efb777a6..363609a83 100644
--- a/app.json
+++ b/app.json
@@ -19,6 +19,11 @@
     "SECRET_TOKEN": {
       "description": "A secret key for verifying the integrity of signed cookies",
       "generator": "secret"
+    },
+    "TZ": {
+      "description": "Timezone (e.g. Asia/Tokyo)",
+      "value": "UTC",
+      "required": false
     }
   },
   "addons": [