diff --git a/packages/backend/src/core/activitypub/ApDbResolverService.ts b/packages/backend/src/core/activitypub/ApDbResolverService.ts
index 062af39732..6905f8bee9 100644
--- a/packages/backend/src/core/activitypub/ApDbResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApDbResolverService.ts
@@ -98,7 +98,10 @@ export class ApDbResolverService implements OnApplicationShutdown {
 	 * AP Person => Misskey User in DB
 	 */
 	@bindThis
-	public async getUserFromApId(value: string | IObject): Promise<MiLocalUser | MiRemoteUser | null> {
+	public async getUserFromApId(value: string | IObject | [string | IObject]): Promise<MiLocalUser | MiRemoteUser | null> {
+		// eslint-disable-next-line no-param-reassign
+		if (Array.isArray(value)) value = value[0];
+
 		const parsed = this.parseUri(value);
 
 		if (parsed.local) {
diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index bce67a458f..289f1606a1 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -253,7 +253,8 @@ export class ApInboxService {
 		}
 
 		if (activity.target === actor.featured) {
-			const note = await this.apNoteService.resolveNote(activity.object);
+			const object = Array.isArray(activity.object) ? activity.object[0] : activity.object;
+			const note = await this.apNoteService.resolveNote(object);
 			if (note == null) return 'note not found';
 			await this.notePiningService.addPinned(actor, note.id);
 			return;
@@ -270,11 +271,12 @@ export class ApInboxService {
 
 		const resolver = this.apResolverService.createResolver();
 
-		if (!activity.object) return 'skip: activity has no object property';
-		const targetUri = getApId(activity.object);
+		const activityObject = Array.isArray(activity.object) ? activity.object[0] : activity.object;
+		if (!activityObject) return 'skip: activity has no object property';
+		const targetUri = getApId(activityObject);
 		if (targetUri.startsWith('bear:')) return 'skip: bearcaps url not supported.';
 
-		const target = await resolver.resolve(activity.object).catch(e => {
+		const target = await resolver.resolve(activityObject).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
 			return e;
 		});
@@ -370,29 +372,30 @@ export class ApInboxService {
 
 		this.logger.info(`Create: ${uri}`);
 
-		if (!activity.object) return 'skip: activity has no object property';
-		const targetUri = getApId(activity.object);
+		const activityObject = Array.isArray(activity.object) ? activity.object[0] : activity.object;
+		if (!activityObject) return 'skip: activity has no object property';
+		const targetUri = getApId(activityObject);
 		if (targetUri.startsWith('bear:')) return 'skip: bearcaps url not supported.';
 
 		// copy audiences between activity <=> object.
-		if (typeof activity.object === 'object') {
-			const to = unique(concat([toArray(activity.to), toArray(activity.object.to)]));
-			const cc = unique(concat([toArray(activity.cc), toArray(activity.object.cc)]));
+		if (typeof activityObject === 'object') {
+			const to = unique(concat([toArray(activity.to), toArray(activityObject.to)]));
+			const cc = unique(concat([toArray(activity.cc), toArray(activityObject.cc)]));
 
 			activity.to = to;
 			activity.cc = cc;
-			activity.object.to = to;
-			activity.object.cc = cc;
+			activityObject.to = to;
+			activityObject.cc = cc;
 		}
 
 		// If there is no attributedTo, use Activity actor.
-		if (typeof activity.object === 'object' && !activity.object.attributedTo) {
-			activity.object.attributedTo = activity.actor;
+		if (typeof activityObject === 'object' && !activityObject.attributedTo) {
+			activityObject.attributedTo = activity.actor;
 		}
 
 		const resolver = this.apResolverService.createResolver();
 
-		const object = await resolver.resolve(activity.object).catch(e => {
+		const object = await resolver.resolve(activityObject).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
 			throw e;
 		});
@@ -448,15 +451,15 @@ export class ApInboxService {
 		// 削除対象objectのtype
 		let formerType: string | undefined;
 
-		if (typeof activity.object === 'string') {
+		const activityObject = Array.isArray(activity.object) ? activity.object[0] : activity.object;
+		if (typeof activityObject === 'string') {
 			// typeが不明だけど、どうせ消えてるのでremote resolveしない
 			formerType = undefined;
 		} else {
-			const object = activity.object;
-			if (isTombstone(object)) {
-				formerType = toSingle(object.formerType);
+			if (isTombstone(activityObject)) {
+				formerType = toSingle(activityObject.formerType);
 			} else {
-				formerType = toSingle(object.type);
+				formerType = toSingle(activityObject.type);
 			}
 		}
 
@@ -616,7 +619,8 @@ export class ApInboxService {
 		}
 
 		if (activity.target === actor.featured) {
-			const note = await this.apNoteService.resolveNote(activity.object);
+			const activityObject = Array.isArray(activity.object) ? activity.object[0] : activity.object;
+			const note = await this.apNoteService.resolveNote(activityObject);
 			if (note == null) return 'note not found';
 			await this.notePiningService.removePinned(actor, note.id);
 			return;
diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index 499a163d6c..ff6f462b4c 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -199,7 +199,8 @@ export class ApRendererService {
 			type: 'Flag',
 			actor: this.userEntityService.genLocalUserUri(user.id),
 			content,
-			object,
+			// This MUST be an array for Pleroma compatibility: https://activitypub.software/TransFem-org/Sharkey/-/issues/641#note_7301
+			object: [object],
 		};
 	}
 
diff --git a/packages/backend/src/core/activitypub/ApResolverService.ts b/packages/backend/src/core/activitypub/ApResolverService.ts
index b047a6c59b..2a803d394d 100644
--- a/packages/backend/src/core/activitypub/ApResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApResolverService.ts
@@ -67,7 +67,10 @@ export class Resolver {
 	}
 
 	@bindThis
-	public async resolve(value: string | IObject): Promise<IObject> {
+	public async resolve(value: string | IObject | [string | IObject]): Promise<IObject> {
+		// eslint-disable-next-line no-param-reassign
+		if (Array.isArray(value)) value = value[0];
+
 		if (typeof value !== 'string') {
 			return value;
 		}
diff --git a/packages/backend/src/core/activitypub/type.ts b/packages/backend/src/core/activitypub/type.ts
index 2f58825de1..2ec3b0baff 100644
--- a/packages/backend/src/core/activitypub/type.ts
+++ b/packages/backend/src/core/activitypub/type.ts
@@ -52,10 +52,13 @@ export function getOneApId(value: ApObject): string {
 /**
  * Get ActivityStreams Object id
  */
-export function getApId(value: string | IObject): string {
+export function getApId(value: string | IObject | [string | IObject]): string {
+	// eslint-disable-next-line no-param-reassign
+	if (Array.isArray(value)) value = value[0];
+
 	if (typeof value === 'string') return value;
 	if (typeof value.id === 'string') return value.id;
-	throw new Error('cannot detemine id');
+	throw new Error('cannot determine id');
 }
 
 /**
@@ -84,7 +87,9 @@ export function getApHrefNullable(value: string | IObject | undefined): string |
 export interface IActivity extends IObject {
 	//type: 'Activity';
 	actor: IObject | string;
-	object: IObject | string;
+	// ActivityPub spec allows for arrays: https://www.w3.org/TR/activitystreams-vocabulary/#properties
+	// Misskey can only handle one value, so we use a tuple for that case.
+	object: IObject | string | [IObject | string] ;
 	target?: IObject | string;
 	/** LD-Signature */
 	signature?: {