diff --git a/examples/glut/main.go b/examples/glut/main.go
index 8baedaa2d..b6ff8ee8d 100644
--- a/examples/glut/main.go
+++ b/examples/glut/main.go
@@ -120,8 +120,8 @@ func (game *DemoGame) Draw(g graphics.GraphicsContext, offscreen graphics.Textur
 		return
 	}
 	geometryMatrix := graphics.IdentityGeometryMatrix()
-	geometryMatrix.SetTx(graphics.AffineMatrixElement(game.x))
-	geometryMatrix.SetTy(graphics.AffineMatrixElement(game.x))
+	geometryMatrix.SetTx(float64(game.x))
+	geometryMatrix.SetTy(float64(game.x))
 	g.DrawTexture(game.ebitenTexture,
 		0, 0, game.ebitenTexture.Width(), game.ebitenTexture.Height(),
 		geometryMatrix,
diff --git a/graphics/affine_matrix.go b/graphics/affine_matrix.go
index b5f20ec31..d2467b550 100644
--- a/graphics/affine_matrix.go
+++ b/graphics/affine_matrix.go
@@ -1,9 +1,9 @@
 package graphics
 
-type AffineMatrixElement float64
+type affineMatrixElement float64
 
 type AffineMatrix struct {
-	elements  []AffineMatrixElement
+	elements  []affineMatrixElement
 	dimension int
 }
 
@@ -13,7 +13,7 @@ func NewAffineMatrix(dimension int) *AffineMatrix {
 	}
 	matrix := &AffineMatrix{}
 	elementsNumber := dimension * (dimension - 1)
-	matrix.elements = make([]AffineMatrixElement, elementsNumber)
+	matrix.elements = make([]affineMatrixElement, elementsNumber)
 	matrix.dimension = dimension
 	return matrix
 }
@@ -41,7 +41,7 @@ func (matrix *AffineMatrix) Clone() *AffineMatrix {
 	return result
 }
 
-func (matrix *AffineMatrix) Element(i, j int) AffineMatrixElement {
+func (matrix *AffineMatrix) Element(i, j int) float64 {
 	dimension := matrix.dimension
 	if i < 0 || dimension <= i {
 		panic("out of range index i")
@@ -55,10 +55,10 @@ func (matrix *AffineMatrix) Element(i, j int) AffineMatrixElement {
 		}
 		return 0
 	}
-	return matrix.elements[i*dimension+j]
+	return float64(matrix.elements[i*dimension+j])
 }
 
-func (matrix *AffineMatrix) SetElement(i, j int, element AffineMatrixElement) {
+func (matrix *AffineMatrix) SetElement(i, j int, element float64) {
 	dimension := matrix.dimension
 	if i < 0 || dimension-1 <= i {
 		panic("out of range index i")
@@ -66,7 +66,7 @@ func (matrix *AffineMatrix) SetElement(i, j int, element AffineMatrixElement) {
 	if j < 0 || dimension <= j {
 		panic("out of range index j")
 	}
-	matrix.elements[i*dimension+j] = element
+	matrix.elements[i*dimension+j] = affineMatrixElement(element)
 }
 
 func (matrix *AffineMatrix) IsIdentity() bool {
@@ -96,7 +96,7 @@ func (rhs *AffineMatrix) Concat(lhs *AffineMatrix) *AffineMatrix {
 
 	for i := 0; i < dimension-1; i++ {
 		for j := 0; j < dimension; j++ {
-			var element AffineMatrixElement = 0.0
+			element := affineMatrixElement(0.0)
 			for k := 0; k < dimension-1; k++ {
 				element += lhs.elements[i*dimension+k] *
 					rhs.elements[k*dimension+j]
diff --git a/graphics/geometry_matrix.go b/graphics/geometry_matrix.go
index 48b5c520e..fbe0381a2 100644
--- a/graphics/geometry_matrix.go
+++ b/graphics/geometry_matrix.go
@@ -18,50 +18,50 @@ func (matrix *GeometryMatrix) Clone() *GeometryMatrix {
 	return &GeometryMatrix{*(matrix.AffineMatrix.Clone())}
 }
 
-func (matrix *GeometryMatrix) A() AffineMatrixElement {
+func (matrix *GeometryMatrix) A() float64 {
 	return matrix.Element(0, 0)
 }
 
-func (matrix *GeometryMatrix) B() AffineMatrixElement {
+func (matrix *GeometryMatrix) B() float64 {
 	return matrix.Element(0, 1)
 }
 
-func (matrix *GeometryMatrix) C() AffineMatrixElement {
+func (matrix *GeometryMatrix) C() float64 {
 	return matrix.Element(1, 0)
 }
 
-func (matrix *GeometryMatrix) D() AffineMatrixElement {
+func (matrix *GeometryMatrix) D() float64 {
 	return matrix.Element(1, 1)
 }
 
-func (matrix *GeometryMatrix) Tx() AffineMatrixElement {
+func (matrix *GeometryMatrix) Tx() float64 {
 	return matrix.Element(0, 2)
 }
 
-func (matrix *GeometryMatrix) Ty() AffineMatrixElement {
+func (matrix *GeometryMatrix) Ty() float64 {
 	return matrix.Element(1, 2)
 }
 
-func (matrix *GeometryMatrix) SetA(a AffineMatrixElement) {
+func (matrix *GeometryMatrix) SetA(a float64) {
 	matrix.SetElement(0, 0, a)
 }
 
-func (matrix *GeometryMatrix) SetB(b AffineMatrixElement) {
+func (matrix *GeometryMatrix) SetB(b float64) {
 	matrix.SetElement(0, 1, b)
 }
 
-func (matrix *GeometryMatrix) SetC(c AffineMatrixElement) {
+func (matrix *GeometryMatrix) SetC(c float64) {
 	matrix.SetElement(1, 0, c)
 }
 
-func (matrix *GeometryMatrix) SetD(d AffineMatrixElement) {
+func (matrix *GeometryMatrix) SetD(d float64) {
 	matrix.SetElement(1, 1, d)
 }
 
-func (matrix *GeometryMatrix) SetTx(tx AffineMatrixElement) {
+func (matrix *GeometryMatrix) SetTx(tx float64) {
 	matrix.SetElement(0, 2, tx)
 }
 
-func (matrix *GeometryMatrix) SetTy(ty AffineMatrixElement) {
+func (matrix *GeometryMatrix) SetTy(ty float64) {
 	matrix.SetElement(1, 2, ty)
 }
diff --git a/graphics/opengl/device.go b/graphics/opengl/device.go
index 9e3223af7..d061eafa0 100644
--- a/graphics/opengl/device.go
+++ b/graphics/opengl/device.go
@@ -54,8 +54,8 @@ func (device *Device) Update() {
 	g.resetOffscreen()
 	g.Clear()
 	geometryMatrix := graphics.IdentityGeometryMatrix()
-	geometryMatrix.SetA(graphics.AffineMatrixElement(g.screenScale))
-	geometryMatrix.SetD(graphics.AffineMatrixElement(g.screenScale))
+	geometryMatrix.SetA(float64(g.screenScale))
+	geometryMatrix.SetD(float64(g.screenScale))
 	g.DrawTexture(device.offscreenTexture,
 		0, 0, device.screenWidth, device.screenHeight,
 		geometryMatrix, graphics.IdentityColorMatrix())