diff --git a/packages/backend/src/queue/processors/InboxProcessorService.ts b/packages/backend/src/queue/processors/InboxProcessorService.ts
index 23e377d790..e790267a04 100644
--- a/packages/backend/src/queue/processors/InboxProcessorService.ts
+++ b/packages/backend/src/queue/processors/InboxProcessorService.ts
@@ -53,6 +53,10 @@ export class InboxProcessorService {
 	@bindThis
 	public async process(job: Bull.Job<InboxJobData>): Promise<string> {
 		const signature = 'version' in job.data.signature ? job.data.signature.value : job.data.signature;
+		if (Array.isArray(signature)) {
+			// RFC 9401はsignatureが配列になるが、とりあえずエラーにする
+			throw new Error('signature is array');
+		}
 		const activity = job.data.activity;
 
 		//#region Log
diff --git a/packages/backend/src/server/api/endpoints/admin/queue/inbox-delayed.ts b/packages/backend/src/server/api/endpoints/admin/queue/inbox-delayed.ts
index 7839d8b6f5..42afa08485 100644
--- a/packages/backend/src/server/api/endpoints/admin/queue/inbox-delayed.ts
+++ b/packages/backend/src/server/api/endpoints/admin/queue/inbox-delayed.ts
@@ -57,7 +57,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 
 			for (const job of jobs) {
 				const signature = 'version' in job.data.signature ? job.data.signature.value : job.data.signature;
-				const host = new URL(signature.keyId).host;
+				const host = Array.isArray(signature) ? 'TODO' : new URL(signature.keyId).host;
 				if (res.find(x => x[0] === host)) {
 					res.find(x => x[0] === host)![1]++;
 				} else {