diff --git a/ui/spacing.go b/ui/spacing.go
index 93ec626..ddd198e 100644
--- a/ui/spacing.go
+++ b/ui/spacing.go
@@ -84,9 +84,16 @@ func (s *Spacing) Center() {
 func (s *Spacing) DesiredSize(ctx Context) geom.PointF32 {
 	var size = s.Proxy.DesiredSize(ctx)
 	var w, h = s.Width.Zero(size.X), s.Height.Zero(size.Y)
+	var margin = func(l *Length) float32 {
+		var v = l.Value()
+		if geom.IsNaN32(v) {
+			return 0
+		}
+		return v
+	}
 	return geom.PtF32(
-		s.Margin.Left.Value()+w+s.Margin.Right.Value(),
-		s.Margin.Top.Value()+h+s.Margin.Bottom.Value())
+		margin(s.Margin.Left)+w+margin(s.Margin.Right),
+		margin(s.Margin.Top)+h+margin(s.Margin.Bottom))
 }
 
 func (s *Spacing) SetSize(w, h float32) {