diff --git a/src/schemas/activitypub.ts b/src/schemas/activitypub.ts
index f14c994f..513457d9 100644
--- a/src/schemas/activitypub.ts
+++ b/src/schemas/activitypub.ts
@@ -154,6 +154,16 @@ const objectSchema = z.union([
   ]),
 );
 
+/** https://docs.joinmastodon.org/entities/Instance/#thumbnail */
+const thumbnailSchema = z.object({
+  url: z.string().url(),
+  blurhash: z.string().optional(),
+  versions: z.object({
+    '@1x': z.string().url().optional(),
+    '@2x': z.string().url().optional(),
+  }).optional(),
+});
+
 const createNoteSchema = z.object({
   type: z.literal('Create'),
   id: apId,
@@ -318,6 +328,7 @@ export type {
   Note,
   Object,
   Proxy,
+  thumbnailSchema,
   Update,
   Zap,
 };