diff --git a/internal/system/canvasbox.go b/internal/system/canvasbox.go
index a59e1e7..c88b3e3 100644
--- a/internal/system/canvasbox.go
+++ b/internal/system/canvasbox.go
@@ -30,6 +30,8 @@ func (this *canvasBox) Invalidate () {
 
 func (this *canvasBox) Draw (can canvas.Canvas) {
 	this.box.Draw(can)
-	this.userDrawer.Draw (
-		can.SubCanvas(this.padding.Apply(this.innerClippingBounds)))
+	if this.userDrawer != nil {
+		this.userDrawer.Draw (
+			can.SubCanvas(this.padding.Apply(this.innerClippingBounds)))
+	}
 }