diff --git a/internal/restorable/image.go b/internal/restorable/image.go
index 25f51a122..18996789e 100644
--- a/internal/restorable/image.go
+++ b/internal/restorable/image.go
@@ -23,6 +23,7 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/affine"
 	"github.com/hajimehoshi/ebiten/internal/graphics"
 	"github.com/hajimehoshi/ebiten/internal/opengl"
+	"github.com/hajimehoshi/ebiten/internal/sync"
 )
 
 // drawImageHistoryItem is an item for history of draw-image commands.
@@ -70,6 +71,8 @@ type Image struct {
 
 	// screen indicates whether the image is used as an actual screen.
 	screen bool
+
+	m sync.Mutex
 }
 
 // NewImage creates an empty image with the given size.
@@ -131,6 +134,9 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 	// For this purpuse, images should remember which part of that is used for DrawImage.
 	theImages.makeStaleIfDependingOn(i)
 
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	i.image.ReplacePixels(pixels, x, y, width, height)
 
 	if x == 0 && y == 0 && width == w && height == h {
@@ -160,11 +166,16 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 
 // DrawImage draws a given image img to the image.
 func (i *Image) DrawImage(img *Image, sx0, sy0, sx1, sy1 int, geom *affine.GeoM, colorm *affine.ColorM, mode opengl.CompositeMode, filter graphics.Filter) {
-	vs := img.vertices(sx0, sy0, sx1, sy1, geom)
+	w, h := img.Size()
+	vs := vertices(w, h, sx0, sy0, sx1, sy1, geom)
 	if vs == nil {
 		return
 	}
 	theImages.makeStaleIfDependingOn(i)
+
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	if img.stale || img.volatile || i.screen || !IsRestoringEnabled() {
 		i.makeStale()
 	} else {
@@ -210,6 +221,10 @@ func (i *Image) At(x, y int) (color.RGBA, error) {
 	if x < 0 || y < 0 || w <= x || h <= y {
 		return color.RGBA{}, nil
 	}
+
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	if err := graphics.FlushCommands(); err != nil {
 		return color.RGBA{}, err
 	}
@@ -225,6 +240,9 @@ func (i *Image) At(x, y int) (color.RGBA, error) {
 
 // makeStaleIfDependingOn makes the image stale if the image depends on target.
 func (i *Image) makeStaleIfDependingOn(target *Image) {
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	if i.stale {
 		return
 	}
@@ -250,6 +268,10 @@ func (i *Image) resolveStale() error {
 	if !IsRestoringEnabled() {
 		return nil
 	}
+
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	if i.volatile {
 		return nil
 	}
@@ -274,6 +296,9 @@ func (i *Image) dependsOn(target *Image) bool {
 
 // dependingImages returns all images that is depended by the image.
 func (i *Image) dependingImages() map[*Image]struct{} {
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	r := map[*Image]struct{}{}
 	for _, c := range i.drawImageHistory {
 		r[c.image] = struct{}{}
@@ -283,6 +308,9 @@ func (i *Image) dependingImages() map[*Image]struct{} {
 
 // hasDependency returns a boolean value indicating whether the image depends on another image.
 func (i *Image) hasDependency() bool {
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	if i.stale {
 		return false
 	}
@@ -291,6 +319,9 @@ func (i *Image) hasDependency() bool {
 
 // Restore restores *graphics.Image from the pixels using its state.
 func (i *Image) restore() error {
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	w, h := i.image.Size()
 	if i.screen {
 		// The screen image should also be recreated because framebuffer might
@@ -348,6 +379,10 @@ func (i *Image) restore() error {
 // After disposing, calling the function of the image causes unexpected results.
 func (i *Image) Dispose() {
 	theImages.remove(i)
+
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	i.image.Dispose()
 	i.image = nil
 	i.basePixels = nil
@@ -364,9 +399,12 @@ func (i *Image) IsInvalidated() (bool, error) {
 	if err := graphics.FlushCommands(); err != nil {
 		return false, err
 	}
-
 	if !IsRestoringEnabled() {
 		return false, nil
 	}
+
+	i.m.Lock()
+	defer i.m.Unlock()
+
 	return i.image.IsInvalidated(), nil
 }
diff --git a/internal/restorable/vertices.go b/internal/restorable/vertices.go
index 2404c5fa5..6cbdc0c18 100644
--- a/internal/restorable/vertices.go
+++ b/internal/restorable/vertices.go
@@ -43,7 +43,7 @@ func (v *verticesBackend) get() []float32 {
 	return s
 }
 
-func (i *Image) vertices(sx0, sy0, sx1, sy1 int, geo *affine.GeoM) []float32 {
+func vertices(width, height int, sx0, sy0, sx1, sy1 int, geo *affine.GeoM) []float32 {
 	if sx0 >= sx1 || sy0 >= sy1 {
 		return nil
 	}
@@ -58,7 +58,6 @@ func (i *Image) vertices(sx0, sy0, sx1, sy1 int, geo *affine.GeoM) []float32 {
 
 	// it really feels like we should be able to cache this computation
 	// but it may not matter.
-	width, height := i.Size()
 	w := 1
 	h := 1
 	for w < width {