diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index b8526a972c..92c91f47de 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -217,6 +217,10 @@ export class ApInboxService {
 		const note = await this.apNoteService.resolveNote(object, { resolver });
 		if (!note) return `skip: target note not found ${targetUri}`;
 
+		if (note.userHost == null && note.localOnly) {
+			throw new IdentifiableError('12e23cec-edd9-442b-aa48-9c21f0c3b215', 'Cannot react to local-only note');
+		}
+
 		await this.apNoteService.extractEmojis(activity.tag ?? [], actor.host).catch(() => null);
 
 		try {
@@ -371,6 +375,10 @@ export class ApInboxService {
 				return 'skip: invalid actor for this activity';
 			}
 
+			if (renote.userHost == null && renote.localOnly) {
+				throw new IdentifiableError('12e23cec-edd9-442b-aa48-9c21f0c3b215', 'Cannot renote a local-only note');
+			}
+
 			this.logger.info(`Creating the (Re)Note: ${uri}`);
 
 			const activityAudience = await this.apAudienceService.parseAudience(actor, activity.to, activity.cc, resolver);
diff --git a/packages/backend/src/core/activitypub/models/ApNoteService.ts b/packages/backend/src/core/activitypub/models/ApNoteService.ts
index 7811b81795..5b66031bee 100644
--- a/packages/backend/src/core/activitypub/models/ApNoteService.ts
+++ b/packages/backend/src/core/activitypub/models/ApNoteService.ts
@@ -285,6 +285,13 @@ export class ApNoteService {
 		const quote = await this.getQuote(note, entryUri, resolver);
 		const processErrors = quote === null ? ['quoteUnavailable'] : null;
 
+		if (reply && reply.userHost == null && reply.localOnly) {
+			throw new IdentifiableError('12e23cec-edd9-442b-aa48-9c21f0c3b215', 'Cannot reply to local-only note');
+		}
+		if (quote && quote.userHost == null && quote.localOnly) {
+			throw new IdentifiableError('12e23cec-edd9-442b-aa48-9c21f0c3b215', 'Cannot quote a local-only note');
+		}
+
 		// vote
 		if (reply && reply.hasPoll) {
 			const poll = await this.pollsRepository.findOneByOrFail({ noteId: reply.id });
@@ -482,6 +489,10 @@ export class ApNoteService {
 		const quote = await this.getQuote(note, entryUri, resolver);
 		const processErrors = quote === null ? ['quoteUnavailable'] : null;
 
+		if (quote && quote.userHost == null && quote.localOnly) {
+			throw new IdentifiableError('12e23cec-edd9-442b-aa48-9c21f0c3b215', 'Cannot quote a local-only note');
+		}
+
 		// vote
 		if (reply && reply.hasPoll) {
 			const poll = await this.pollsRepository.findOneByOrFail({ noteId: reply.id });