diff --git a/20.md b/20.md
index 1f06fa95..447b10a0 100644
--- a/20.md
+++ b/20.md
@@ -21,6 +21,8 @@ The `message` SHOULD provide additional information as to why the command succee
 
 The `message` SHOULD start with `blocked:` if the pubkey or network address has been blocked, banned or is not on a whitelist.
 
+The `message` SHOULD start with `invalid:` if the event doesn't meet some specific criteria (created_at is too far off, etc)
+
 The `message` SHOULD start with `rate-limited:` if the event was rejected due to rate limiting techniques.
 
 Ephemeral events are not acknowledged with OK responses, unless there is a failure.
@@ -55,6 +57,10 @@ Event rejected, rate limited
 
     ["OK", "b1a649ebe8...", false, "rate-limited: slow down there chief"]
 
+Event rejected, `created_at` too far off
+
+    ["OK", "b1a649ebe8...", false, "invalid: event creation date is too far off from the current time. Is your system clock in sync?"]
+
 
 
 Future Extensions