diff --git a/dbus/run.go b/dbus/run.go
index eef0d14..0b8267f 100644
--- a/dbus/run.go
+++ b/dbus/run.go
@@ -2,14 +2,14 @@ package dbus
 
 import (
 	"errors"
-	"os"
+	"io"
 
 	"git.ophivana.moe/cat/fortify/helper"
 )
 
 // Start launches the D-Bus proxy and sets up the Wait method.
 // ready should be buffered and should only be received from once.
-func (p *Proxy) Start(ready chan error, output bool) error {
+func (p *Proxy) Start(ready chan error, output io.Writer) error {
 	p.lock.Lock()
 	defer p.lock.Unlock()
 
@@ -25,9 +25,9 @@ func (p *Proxy) Start(ready chan error, output bool) error {
 	// xdg-dbus-proxy does not need to inherit the environment
 	h.Env = []string{}
 
-	if output {
-		h.Stdout = os.Stdout
-		h.Stderr = os.Stderr
+	if output != nil {
+		h.Stdout = output
+		h.Stderr = output
 	}
 	if err := h.StartNotify(ready); err != nil {
 		return err
diff --git a/internal/app/share.dbus.go b/internal/app/share.dbus.go
index e94d648..b1be631 100644
--- a/internal/app/share.dbus.go
+++ b/internal/app/share.dbus.go
@@ -102,7 +102,7 @@ func (tx *appSealTx) startDBus() error {
 	tx.dbusWait = make(chan struct{})
 
 	// background dbus proxy start
-	if err := tx.dbus.Start(ready, true); err != nil {
+	if err := tx.dbus.Start(ready, os.Stderr); err != nil {
 		return (*StartDBusError)(wrapError(err, "cannot start message bus proxy:", err))
 	}
 	verbose.Println("starting message bus proxy:", tx.dbus)