diff --git a/packages/backend/src/remote/activitypub/request.ts b/packages/backend/src/remote/activitypub/request.ts
index 197f7579b..0bb196250 100644
--- a/packages/backend/src/remote/activitypub/request.ts
+++ b/packages/backend/src/remote/activitypub/request.ts
@@ -121,9 +121,10 @@ export async function signedGet(_url: string, user: { id: User['id'] }): Promise
 				return false;
 			};
 
-			if (isActivitypub(res.headers.get('Content-Type'))) {
-				return await res.json();
+			if (!isActivitypub(res.headers.get('Content-Type'))) {
+				throw new Error('invalid response content type');
 			}
+			return await res.json();
 		}
 	}