diff --git a/image.go b/image.go
index a13931fa9..6022d507f 100644
--- a/image.go
+++ b/image.go
@@ -98,15 +98,11 @@ func (t *textureQuads) Texture(i int) (u0, v0, u1, v1 float32) {
 	return u(float64(src.Min.X), w), v(float64(src.Min.Y), h), u(float64(src.Max.X), w), v(float64(src.Max.Y), h)
 }
 
-type syncer interface {
-	Sync(func())
-}
-
 // Image represents an image.
 // The pixel format is alpha-premultiplied.
 // Image implements image.Image.
 type Image struct {
-	syncer syncer
+	ui     *ui
 	inner  *innerImage
 	pixels []uint8
 }
@@ -119,8 +115,8 @@ func (i *Image) Size() (width, height int) {
 // Clear resets the pixels of the image into 0.
 func (i *Image) Clear() (err error) {
 	i.pixels = nil
-	i.syncer.Sync(func() {
-		err = i.inner.Clear(currentUI.glContext)
+	i.ui.use(func() {
+		err = i.inner.Clear(i.ui.glContext)
 	})
 	return
 }
@@ -128,8 +124,8 @@ func (i *Image) Clear() (err error) {
 // Fill fills the image with a solid color.
 func (i *Image) Fill(clr color.Color) (err error) {
 	i.pixels = nil
-	i.syncer.Sync(func() {
-		err = i.inner.Fill(currentUI.glContext, clr)
+	i.ui.use(func() {
+		err = i.inner.Fill(i.ui.glContext, clr)
 	})
 	return
 }
@@ -151,8 +147,8 @@ func (i *Image) DrawImage(image *Image, options *DrawImageOptions) (err error) {
 
 func (i *Image) drawImage(image *innerImage, option *DrawImageOptions) (err error) {
 	i.pixels = nil
-	i.syncer.Sync(func() {
-		err = i.inner.drawImage(currentUI.glContext, image, option)
+	i.ui.use(func() {
+		err = i.inner.drawImage(i.ui.glContext, image, option)
 	})
 	return
 }
@@ -173,9 +169,9 @@ func (i *Image) ColorModel() color.Model {
 // This method loads pixels from GPU to VRAM if necessary.
 func (i *Image) At(x, y int) color.Color {
 	if i.pixels == nil {
-		i.syncer.Sync(func() {
+		i.ui.use(func() {
 			var err error
-			i.pixels, err = i.inner.texture.Pixels(currentUI.glContext)
+			i.pixels, err = i.inner.texture.Pixels(i.ui.glContext)
 			if err != nil {
 				panic(err)
 			}
diff --git a/run.go b/run.go
index 44fe236a8..c3e20d2a1 100644
--- a/run.go
+++ b/run.go
@@ -28,18 +28,12 @@ import (
 // but this is not strictly guaranteed.
 // If you need to care about time, you need to check current time every time f is called.
 func Run(f func(*Image) error, width, height, scale int, title string) error {
-	err := startUI(width, height, scale, title)
+	ui, err := startUI(width, height, scale, title)
 	if err != nil {
 		return err
 	}
-	ui := currentUI
 	defer ui.terminate()
 
-	currentUI = ui
-	defer func() {
-		currentUI = nil
-	}()
-
 	for {
 		// To avoid busy loop when the window is inactive, wait 1/120 [sec] at least.
 		ch := time.After(1 * time.Second / 120)
diff --git a/ui.go b/ui.go
index 86974f0ab..472287d61 100644
--- a/ui.go
+++ b/ui.go
@@ -42,15 +42,16 @@ func init() {
 		panic(err)
 	}
 
-	currentUI = &ui{
+	u := &ui{
 		window: window,
 		funcs:  make(chan func()),
 	}
-	currentUI.run()
-	currentUI.use(func() {
-		currentUI.glContext = opengl.NewContext()
+	u.run()
+	u.use(func() {
+		u.glContext = opengl.NewContext()
 		glfw.SwapInterval(1)
 	})
+	currentUI = u
 }
 
 type ui struct {
@@ -62,20 +63,21 @@ type ui struct {
 	funcs           chan func()
 }
 
-func startUI(width, height, scale int, title string) error {
+func startUI(width, height, scale int, title string) (*ui, error) {
 	monitor, err := glfw.GetPrimaryMonitor()
 	if err != nil {
-		return err
+		return nil, err
 	}
 	videoMode, err := monitor.GetVideoMode()
 	if err != nil {
-		return err
+		return nil, err
 	}
 	x := (videoMode.Width - width*scale) / 2
 	y := (videoMode.Height - height*scale) / 3
 
 	ch := make(chan struct{})
-	window := currentUI.window
+	ui := currentUI
+	window := ui.window
 	window.SetFramebufferSizeCallback(func(w *glfw.Window, width, height int) {
 		close(ch)
 	})
@@ -97,7 +99,6 @@ func startUI(width, height, scale int, title string) error {
 		}
 	}
 
-	ui := currentUI
 	ui.scale = scale
 
 	// For retina displays, recalculate the scale with the framebuffer size.
@@ -106,7 +107,7 @@ func startUI(width, height, scale int, title string) error {
 	ui.use(func() {
 		ui.graphicsContext, err = newGraphicsContext(ui.glContext, width, height, realScale)
 	})
-	return err
+	return ui, err
 }
 
 func (u *ui) doEvents() {
@@ -122,10 +123,6 @@ func (u *ui) isClosed() bool {
 	return u.window.ShouldClose()
 }
 
-func (u *ui) Sync(f func()) {
-	u.use(f)
-}
-
 func (u *ui) draw(f func(*Image) error) (err error) {
 	u.use(func() {
 		err = u.graphicsContext.preUpdate()
@@ -133,7 +130,7 @@ func (u *ui) draw(f func(*Image) error) (err error) {
 	if err != nil {
 		return
 	}
-	err = f(&Image{syncer: u, inner: u.graphicsContext.screen})
+	err = f(&Image{ui: u, inner: u.graphicsContext.screen})
 	if err != nil {
 		return
 	}
@@ -161,7 +158,7 @@ func (u *ui) newImageFromImage(img image.Image, filter Filter) (*Image, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &Image{syncer: u, inner: innerImage}, nil
+	return &Image{ui: u, inner: innerImage}, nil
 }
 
 func (u *ui) newImage(width, height int, filter Filter) (*Image, error) {
@@ -179,7 +176,7 @@ func (u *ui) newImage(width, height int, filter Filter) (*Image, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &Image{syncer: u, inner: innerImage}, nil
+	return &Image{ui: u, inner: innerImage}, nil
 }
 
 func (u *ui) run() {