diff --git a/captcha.go b/captcha.go
index 19ad554..da857b4 100644
--- a/captcha.go
+++ b/captcha.go
@@ -136,11 +136,7 @@ func New(width int, height int, option ...SetOption) (*Data, error) {
 
 	text := randomText(options)
 	img := image.NewNRGBA(image.Rect(0, 0, width, height))
-	draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.Point{}, draw.Src)
-	drawNoise(img, options)
-	drawCurves(img, options)
-	err := drawText(text, img, options)
-	if err != nil {
+	if err := drawWithOption(text, img, options); err != nil {
 		return nil, err
 	}
 
@@ -157,11 +153,7 @@ func NewMathExpr(width int, height int, option ...SetOption) (*Data, error) {
 
 	text, equation := randomEquation()
 	img := image.NewNRGBA(image.Rect(0, 0, width, height))
-	draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.Point{}, draw.Src)
-	drawNoise(img, options)
-	drawCurves(img, options)
-	err := drawText(equation, img, options)
-	if err != nil {
+	if err := drawWithOption(equation, img, options); err != nil {
 		return nil, err
 	}
 
@@ -179,17 +171,20 @@ func NewCustomGenerator(
 
 	answer, question := generator()
 	img := image.NewNRGBA(image.Rect(0, 0, width, height))
-	draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.Point{}, draw.Src)
-	drawNoise(img, options)
-	drawCurves(img, options)
-	err := drawText(question, img, options)
-	if err != nil {
+	if err := drawWithOption(question, img, options); err != nil {
 		return nil, err
 	}
 
 	return &Data{Text: answer, img: img}, nil
 }
 
+func drawWithOption(text string, img *image.NRGBA, options *Options) error {
+	draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.Point{}, draw.Src)
+	drawNoise(img, options)
+	drawCurves(img, options)
+	return drawText(text, img, options)
+}
+
 func randomText(opts *Options) (text string) {
 	n := len(opts.CharPreset)
 	for i := 0; i < opts.TextLength; i++ {
diff --git a/captcha_test.go b/captcha_test.go
index c116c74..e75630e 100644
--- a/captcha_test.go
+++ b/captcha_test.go
@@ -69,6 +69,12 @@ func TestNewCaptchaOptions(t *testing.T) {
 	NewMathExpr(100, 34, func(options *Options) {
 		options.BackgroundColor = color.Black
 	})
+
+	NewCustomGenerator(100, 34, func() (anwser string, question string) {
+		return "4", "2x2?"
+	}, func(o *Options) {
+		o.BackgroundColor = color.Black
+	})
 }
 
 func TestNewMathExpr(t *testing.T) {
@@ -101,6 +107,13 @@ func TestNilFontError(t *testing.T) {
 		t.Fatal("Expect to get nil font error")
 	}
 
+	_, err = NewCustomGenerator(150, 50, func() (anwser string, question string) {
+		return "1", "2"
+	})
+	if err == nil {
+		t.Fatal("Expect to get nil font error")
+	}
+
 	ttfFont = temp
 }