diff --git a/internal/captcha/dwelling_captcha.go b/internal/captcha/dwelling_captcha.go
index 82110d5..a5eb7d0 100644
--- a/internal/captcha/dwelling_captcha.go
+++ b/internal/captcha/dwelling_captcha.go
@@ -26,10 +26,11 @@ func NewDwellingCaptcha(expiry time.Duration) *DwellingCaptcha {
 }
 
 func (c *DwellingCaptcha) generateImage(style string) *image.Image {
+	isDark := style == "dark"
 	ctx := gg.NewContext(dwImageWidth, dwImageHeight)
 
 	// fill background
-	if style == "dark" {
+	if isDark {
 		ctx.SetRGB255(0x0a, 0x0a, 0x0a)
 	} else {
 		ctx.SetRGB255(0xf5, 0xf5, 0xf5)
@@ -37,7 +38,7 @@ func (c *DwellingCaptcha) generateImage(style string) *image.Image {
 	ctx.Clear()
 
 	// draw text
-	if style == "dark" {
+	if isDark {
 		ctx.SetRGB255(0xf5, 0xf5, 0xf5)
 	} else {
 		ctx.SetRGB255(0x0a, 0x0a, 0x0a)