diff --git a/cue/types.go b/cue/types.go
index afc5beebb39..ea58c65dc8f 100644
--- a/cue/types.go
+++ b/cue/types.go
@@ -110,10 +110,9 @@ func (o *hiddenStructValue) At(i int) (key string, v Value) {
 	return o.v.idx.LabelStr(f), newChildValue(o, i)
 }
 
-func (o *hiddenStructValue) at(i int) (v *adt.Vertex, isOpt bool) {
+func (o *hiddenStructValue) at(i int) *adt.Vertex {
 	f := o.features[i]
-	arc := o.obj.Lookup(f)
-	return arc, arc.IsConstraint()
+	return o.obj.Lookup(f)
 }
 
 // Lookup reports the field for the given key. The returned Value is invalid
@@ -215,7 +214,7 @@ type Iterator struct {
 	val   Value
 	idx   *runtime.Runtime
 	ctx   *adt.OpContext
-	arcs  []field
+	arcs  []*adt.Vertex
 	p     int
 	cur   Value
 	f     adt.Feature
@@ -224,11 +223,6 @@ type Iterator struct {
 
 type hiddenIterator = Iterator
 
-type field struct {
-	arc        *adt.Vertex
-	isOptional bool
-}
-
 // Next advances the iterator to the next value and reports whether there was
 // any. It must be called before the first call to Value or Key.
 func (i *Iterator) Next() bool {
@@ -236,12 +230,12 @@ func (i *Iterator) Next() bool {
 		i.cur = Value{}
 		return false
 	}
-	f := i.arcs[i.p]
-	f.arc.Finalize(i.ctx)
-	p := linkParent(i.val.parent_, i.val.v, f.arc)
-	i.cur = makeValue(i.val.idx, f.arc, p)
-	i.f = f.arc.Label
-	i.isOpt = f.isOptional
+	arc := i.arcs[i.p]
+	arc.Finalize(i.ctx)
+	p := linkParent(i.val.parent_, i.val.v, arc)
+	i.cur = makeValue(i.val.idx, arc, p)
+	i.f = arc.Label
+	i.isOpt = arc.ArcType == adt.ArcOptional
 	i.p++
 	return true
 }
@@ -630,7 +624,7 @@ func newValueRoot(idx *runtime.Runtime, ctx *adt.OpContext, x adt.Expr) Value {
 }
 
 func newChildValue(o *structValue, i int) Value {
-	arc, _ := o.at(i)
+	arc := o.at(i)
 	return makeValue(o.v.idx, arc, linkParent(o.v.parent_, o.v.v, arc))
 }
 
@@ -1284,10 +1278,10 @@ func (v Value) List() (Iterator, error) {
 	if err := v.checkKind(ctx, adt.ListKind); err != nil {
 		return Iterator{idx: v.idx, ctx: ctx}, v.toErr(err)
 	}
-	arcs := []field{}
+	arcs := []*adt.Vertex{}
 	for _, a := range v.v.Elems() {
 		if a.Label.IsInt() {
-			arcs = append(arcs, field{arc: a})
+			arcs = append(arcs, a)
 		}
 	}
 	return Iterator{idx: v.idx, ctx: ctx, val: v, arcs: arcs}, nil
@@ -1467,7 +1461,8 @@ func (s *hiddenStruct) Len() int {
 
 // field reports information about the ith field, i < o.Len().
 func (s *hiddenStruct) Field(i int) FieldInfo {
-	a, opt := s.at(i)
+	a := s.at(i)
+	opt := a.ArcType == adt.ArcOptional
 	ctx := s.v.ctx()
 
 	v := makeChildValue(s.v, a)
@@ -1506,10 +1501,10 @@ func (v Value) Fields(opts ...Option) (*Iterator, error) {
 		return &Iterator{idx: v.idx, ctx: ctx}, v.toErr(err)
 	}
 
-	arcs := []field{}
+	arcs := []*adt.Vertex{}
 	for i := range obj.features {
-		arc, isOpt := obj.at(i)
-		arcs = append(arcs, field{arc: arc, isOptional: isOpt})
+		arc := obj.at(i)
+		arcs = append(arcs, arc)
 	}
 	return &Iterator{idx: v.idx, ctx: ctx, val: v, arcs: arcs}, nil
 }