diff --git a/api/webhook/interactionserver.go b/api/webhook/interactionserver.go
index 02741b8..08bc898 100644
--- a/api/webhook/interactionserver.go
+++ b/api/webhook/interactionserver.go
@@ -31,6 +31,8 @@ func writeError(w http.ResponseWriter, code int, err error) {
 		log.Panicln("cannot marshal error response:", err)
 	}
 
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(code)
 	w.Write(b)
 }