diff --git a/src/activitypub/notes.js b/src/activitypub/notes.js
index 9758b1a73d..21aebb4c63 100644
--- a/src/activitypub/notes.js
+++ b/src/activitypub/notes.js
@@ -340,8 +340,9 @@ Notes.assertPrivate = async (object) => {
 	const payload = await activitypub.mocks.message(object);
 
 	// Naive image appending (using src/posts/attachments.js is likely better, but not worth the effort)
-	if (payload._activitypub.hasOwnProperty('attachment')) {
-		const images = payload._activitypub.attachment.filter((attachment) => {
+	const attachments = payload._activitypub.attachment;
+	if (attachments && Array.isArray(attachments)) {
+		const images = attachments.filter((attachment) => {
 			return attachment.mediaType.startsWith('image/');
 		}).map(({ url, href }) => url || href);
 		images.forEach((url) => {