diff --git a/packages/backend/src/queue/processors/WebhookDeliverProcessorService.ts b/packages/backend/src/queue/processors/WebhookDeliverProcessorService.ts
index 39b1b9565..84a5c21c4 100644
--- a/packages/backend/src/queue/processors/WebhookDeliverProcessorService.ts
+++ b/packages/backend/src/queue/processors/WebhookDeliverProcessorService.ts
@@ -39,6 +39,7 @@ export class WebhookDeliverProcessorService {
 					'X-Misskey-Host': this.config.host,
 					'X-Misskey-Hook-Id': job.data.webhookId,
 					'X-Misskey-Hook-Secret': job.data.secret,
+					'Content-Type': 'application/json',
 				},
 				body: JSON.stringify({
 					hookId: job.data.webhookId,