diff --git a/api/label/iterator.go b/api/label/iterator.go
index ca852d500..f4870f5dd 100644
--- a/api/label/iterator.go
+++ b/api/label/iterator.go
@@ -91,13 +91,12 @@ func (i *Iterator) ToSlice() []kv.KeyValue {
 	return slice
 }
 
-// NewMergeIterator returns a MergeIterator for merging two label set
-// iterators.  Duplicates are resolved by taking the value from the
-// first iterator.
-func NewMergeIterator(iter1, iter2 Iterator) MergeItererator {
+// NewMergeIterator returns a MergeIterator for merging two label sets
+// Duplicates are resolved by taking the value from the first set.
+func NewMergeIterator(s1, s2 *Set) MergeItererator {
 	mi := MergeItererator{
-		one: makeOne(iter1),
-		two: makeOne(iter2),
+		one: makeOne(s1.Iter()),
+		two: makeOne(s2.Iter()),
 	}
 	return mi
 }
diff --git a/sdk/resource/resource.go b/sdk/resource/resource.go
index 8599f04bd..d45f30d15 100644
--- a/sdk/resource/resource.go
+++ b/sdk/resource/resource.go
@@ -89,15 +89,24 @@ func (r *Resource) Equal(eq *Resource) bool {
 // If there are common keys between resource a and b, then the value
 // from resource a is preserved.
 func Merge(a, b *Resource) *Resource {
+	if a == nil && b == nil {
+		return Empty()
+	}
 	if a == nil {
-		a = Empty()
+		return b
 	}
 	if b == nil {
-		b = Empty()
+		return a
 	}
+
 	// Note: 'b' is listed first so that 'a' will overwrite with
 	// last-value-wins in label.Key()
-	combine := append(b.Attributes(), a.Attributes()...)
+	// combine := append(b.Attributes(), a.Attributes()...)
+	mi := label.NewMergeIterator(a.LabelSet(), b.LabelSet())
+	combine := make([]kv.KeyValue, 0, a.Len()+b.Len())
+	for mi.Next() {
+		combine = append(combine, mi.Label())
+	}
 	return New(combine...)
 }
 
@@ -111,10 +120,15 @@ func Empty() *Resource {
 // between two resources.  This value is suitable for use as a key in
 // a map.
 func (r *Resource) Equivalent() label.Distinct {
+	return r.LabelSet().Equivalent()
+}
+
+// LabelSet returns the equivalent *label.Set.
+func (r *Resource) LabelSet() *label.Set {
 	if r == nil {
 		r = Empty()
 	}
-	return r.labels.Equivalent()
+	return &r.labels
 }
 
 // MarshalJSON encodes labels as a JSON list of { "Key": "...", "Value": ... }