diff --git a/40.md b/40.md
index 5f67732e..b8140128 100644
--- a/40.md
+++ b/40.md
@@ -25,7 +25,7 @@ options:
     "created_at": 1000000000,
     "kind": 1,
     "tags": [
-      ["expiration", 1600000000]
+      ["expiration", "1600000000"]
     ],
     "content": "This message will expire at the specified timestamp and be deleted by relays.\n",
     "id": "<event-id>"