diff --git a/roaring/roaring.go b/roaring/roaring.go
index 587cc5f7b..503046690 100644
--- a/roaring/roaring.go
+++ b/roaring/roaring.go
@@ -1756,6 +1756,14 @@ type RoaringIterator interface {
 	// Clone copies the iterator, preserving it at this point in the iteration.
 	// It may well share much underlying data.
 	Clone() RoaringIterator
+
+	// ContainerKeySpan provides the smallest and largest
+	// container keys that the iterator will return.
+	// The current implementation requires that the underlying header
+	// lists the keys in ascending order.
+	// Iff there no keys, then empty will be returned true.
+	// If there is only a single key, then ckeyLast will equal ckeyFirst.
+	ContainerKeySpan() (ckeyFirst, ckeyLast uint64, empty bool)
 }
 
 // baseRoaringIterator holds values used by both Pilosa and official Roaring
@@ -1924,6 +1932,22 @@ func (r *baseRoaringIterator) Done(err error) {
 	r.currentDataOffset = 0
 }
 
+func (r *baseRoaringIterator) ContainerKeySpan() (ckeyFirst, ckeyLast uint64, empty bool) {
+	n := r.keys
+	if n == 0 {
+		empty = true
+		return
+	}
+	ckeyFirst = binary.LittleEndian.Uint64(r.headers[0:8])
+	if n == 1 {
+		ckeyLast = ckeyFirst
+		return
+	}
+	beg := (n - 1) * 12
+	ckeyLast = binary.LittleEndian.Uint64(r.headers[beg : beg+8])
+	return
+}
+
 // Len() indicates the total number of containers the iterator expects to have.
 func (r *baseRoaringIterator) Len() int64 {
 	return r.keys
diff --git a/roaring/roaring_internal_test.go b/roaring/roaring_internal_test.go
index e924b63a6..a7575121d 100644
--- a/roaring/roaring_internal_test.go
+++ b/roaring/roaring_internal_test.go
@@ -4430,6 +4430,17 @@ func TestCloneRoaringIterator(t *testing.T) {
 
 	itr2 := itr.Clone()
 
+	firstCkey, lastCkey, empty := itr2.ContainerKeySpan()
+	if empty {
+		t.Fatalf("should not be empty")
+	}
+	if firstCkey != 0 {
+		t.Fatalf("firstCkey should be 0")
+	}
+	if lastCkey != 10001 {
+		t.Fatalf("lastCkey should be 10001")
+	}
+
 	var keys []uint64
 	for itrKey, synthC := itr.NextContainer(); synthC != nil; itrKey, synthC = itr.NextContainer() {
 		keys = append(keys, itrKey)
@@ -4446,6 +4457,54 @@ func TestCloneRoaringIterator(t *testing.T) {
 	}
 }
 
+func TestRoaringIteratorContainerKeySpan(t *testing.T) {
+
+	ca := NewContainerArray([]uint16{1, 10, 100, 1000})
+	ba := NewFileBitmap()
+	ba.Containers.Put(101, ca)
+	ba.Containers.Put(10, ca)
+	ba.Containers.Put(10001, ca)
+	var buf bytes.Buffer
+	_, err := ba.WriteTo(&buf)
+	if err != nil {
+		t.Fatalf("error writing: %v", err)
+	}
+
+	itr, err := NewRoaringIterator(buf.Bytes())
+	if err != nil {
+		t.Fatalf("error NewRoaringIterator(buf.Bytes()): %v", err)
+	}
+
+	firstCkey, lastCkey, empty := itr.ContainerKeySpan()
+	if empty {
+		t.Fatalf("should not be empty")
+	}
+	if firstCkey != 10 {
+		t.Fatalf("firstCkey should be 10")
+	}
+	if lastCkey != 10001 {
+		t.Fatalf("lastCkey should be 10001")
+	}
+
+	// make and check empty bitmap
+
+	baEmpty := NewFileBitmap()
+	var bufEmpty bytes.Buffer
+	_, err = baEmpty.WriteTo(&bufEmpty)
+	if err != nil {
+		t.Fatalf("error writing: %v", err)
+	}
+
+	itrEmpty, err := NewRoaringIterator(bufEmpty.Bytes())
+	if err != nil {
+		t.Fatalf("error NewRoaringIterator(bufEmpty.Bytes()): %v", err)
+	}
+	_, _, empty = itrEmpty.ContainerKeySpan()
+	if !empty {
+		t.Fatalf("should be empty")
+	}
+}
+
 // we were seeing unionInterval16InPlace() returning too
 // large an run container, which was causing problems when
 // we write to the transactional backends. Verify that