diff --git a/shader/crt_basic.go b/shader/crt_basic.go
index f8ad08c..84b580b 100644
--- a/shader/crt_basic.go
+++ b/shader/crt_basic.go
@@ -87,6 +87,9 @@ type CrtBasic struct {
 }
 
 func (b *CrtBasic) Apply(screen *ebiten.Image, buffer *ebiten.Image) error {
+	b.Lock()
+	defer b.Unlock()
+
 	b.tick += 1 / 60.0
 	var options ebiten.DrawRectShaderOptions
 	options.GeoM.Translate(0, 0)
diff --git a/shader/crt_lotte.go b/shader/crt_lotte.go
index c3f1b0d..fa21431 100644
--- a/shader/crt_lotte.go
+++ b/shader/crt_lotte.go
@@ -310,6 +310,9 @@ type CrtLotte struct {
 }
 
 func (s *CrtLotte) Apply(screen *ebiten.Image, buffer *ebiten.Image) error {
+	s.Lock()
+	defer s.Unlock()
+
 	s.Uniforms["ScreenSize"] = []float32{float32(screen.Bounds().Dx()), float32(screen.Bounds().Dy())}
 	s.Uniforms["TextureSize"] = []float32{float32(buffer.Bounds().Dx()), float32(buffer.Bounds().Dy())}
 
diff --git a/shader/shader.go b/shader/shader.go
index 4669cf9..a1be376 100644
--- a/shader/shader.go
+++ b/shader/shader.go
@@ -1,17 +1,24 @@
 package shader
 
-import "github.com/hajimehoshi/ebiten/v2"
+import (
+	"github.com/hajimehoshi/ebiten/v2"
+	"sync"
+)
 
 type Shader interface {
 	Apply(screen *ebiten.Image, buffer *ebiten.Image) error
 }
 
 type BaseShader struct {
+	sync.Mutex
 	Shader   *ebiten.Shader
 	Uniforms map[string]any
 }
 
 func (b *BaseShader) Apply(screen *ebiten.Image, buffer *ebiten.Image) error {
+	b.Lock()
+	defer b.Unlock()
+
 	var options ebiten.DrawRectShaderOptions
 	options.GeoM.Translate(0, 0)
 	options.Images[0] = buffer