diff --git a/packages/backend/src/remote/activitypub/models/person.ts b/packages/backend/src/remote/activitypub/models/person.ts
index c15e33dbe..c663cdd9c 100644
--- a/packages/backend/src/remote/activitypub/models/person.ts
+++ b/packages/backend/src/remote/activitypub/models/person.ts
@@ -301,7 +301,7 @@ export async function createPerson(
 					tags,
 					isBot,
 					isCat: (person as any).isCat === true,
-					speakAsCat: person.speakAsCat,
+					speakAsCat: (person as any).speakAsCat === true,
 					isIndexable: person.indexable,
 				}),
 			)) as IRemoteUser;
@@ -545,6 +545,7 @@ export async function updatePerson(
 		tags,
 		isBot: getApType(object) !== "Person",
 		isCat: (person as any).isCat === true,
+		speakAsCat: (person as any).speakAsCat === true,
 		isIndexable: person.indexable,
 		isLocked: !!person.manuallyApprovesFollowers,
 		movedToUri: person.movedTo || null,
diff --git a/packages/backend/src/remote/activitypub/renderer/index.ts b/packages/backend/src/remote/activitypub/renderer/index.ts
index bb5dcdfc1..dc8e1325e 100644
--- a/packages/backend/src/remote/activitypub/renderer/index.ts
+++ b/packages/backend/src/remote/activitypub/renderer/index.ts
@@ -35,6 +35,9 @@ export const renderActivity = (x: any): IActivity | null => {
 					schema: "http://schema.org#",
 					PropertyValue: "schema:PropertyValue",
 					value: "schema:value",
+					// Firefish
+					firefish: "https://joinfirefish.org/ns#",
+					speakAsCat: "firefish:speakAsCat",
 					// Misskey
 					misskey: "https://misskey-hub.net/ns#",
 					_misskey_content: "misskey:_misskey_content",