diff --git a/d2themes/sketch_overlay.go b/d2themes/sketch_overlay.go
index f1557c623..65ccde356 100644
--- a/d2themes/sketch_overlay.go
+++ b/d2themes/sketch_overlay.go
@@ -24,9 +24,15 @@ func (o *ThemableSketchOverlay) Render() (string, error) {
 	if color.IsThemeColor(o.fill) {
 		o.el.ClassName += fmt.Sprintf(" sketch-overlay-%s", o.fill) // e.g. sketch-overlay-B3
 	} else {
-		lc, err := color.LuminanceCategory(o.fill)
-		if err != nil {
-			return "", err
+		var lc string
+		if color.IsUrlGradientId(o.fill) {
+			lc = "normal"
+		} else {
+			var err error
+			lc, err = color.LuminanceCategory(o.fill)
+			if err != nil {
+				return "", err
+			}
 		}
 		o.el.ClassName += fmt.Sprintf(" sketch-overlay-%s", lc) // e.g. sketch-overlay-dark
 	}
diff --git a/lib/color/gradient.go b/lib/color/gradient.go
index 29f29acc3..6b308b440 100644
--- a/lib/color/gradient.go
+++ b/lib/color/gradient.go
@@ -246,3 +246,9 @@ var GradientRegex = regexp.MustCompile(`^(linear|radial)-gradient\((.+)\)$`)
 func IsGradient(color string) bool {
 	return GradientRegex.MatchString(color)
 }
+
+var UrlGradientId = regexp.MustCompile(`^url\('#grad-[a-f0-9]{40}'\)$`)
+
+func IsUrlGradientId(color string) bool {
+	return UrlGradientId.MatchString(color)
+}