diff --git a/client/coral-framework/graphql/mutations.js b/client/coral-framework/graphql/mutations.js
index f34a2cc88..1b3b4c6fc 100644
--- a/client/coral-framework/graphql/mutations.js
+++ b/client/coral-framework/graphql/mutations.js
@@ -698,7 +698,7 @@ export const withCloseAsset = withMutation(
             const fragmentId = `Asset_${id}`;
             const data = {
               __typename: 'Asset',
-              closedAt: new Date(),
+              closedAt: new Date().toISOString(),
               isClosed: true,
             };
             proxy.writeFragment({ fragment, id: fragmentId, data });