diff --git a/deno/logging.ts b/deno/logging.ts
index 6e629f8..d95ecac 100644
--- a/deno/logging.ts
+++ b/deno/logging.ts
@@ -7,7 +7,7 @@ type MessageSource = "logging" | "diagnostic" | "user";
 
 type Message = {
     // FIXME: number probably isn't what we want here
-    timestamp: number;
+    timestamp?: number;
     source: MessageSource;
 
     text: AtLeastOne<string>;