diff --git a/src/lexicons/site.standard.graph.subscription.ts b/src/lexicons/site.standard.graph.subscription.ts
index c24a50a..b8eb3ec 100644
--- a/src/lexicons/site.standard.graph.subscription.ts
+++ b/src/lexicons/site.standard.graph.subscription.ts
@@ -9,6 +9,9 @@ export const siteStandardGraphSubscription = lx.lexicon('site.standard.graph.sub
                 required: true,
                 format: 'at-uri',
                 description: 'AT-URI reference to the publication record being subscribed to (ex: at://did:plc:abc123/site.standard.publication/xyz789).'
+            }),
+            createdAt: lx.string({
+                format: "datetime"
             })
         }),
         description: 'Record declaring a subscription to a publication.'