diff --git a/bitmapcontainer.go b/bitmapcontainer.go
index 416da732..1ef8e3e4 100644
--- a/bitmapcontainer.go
+++ b/bitmapcontainer.go
@@ -187,10 +187,17 @@ func (bcmi *bitmapContainerManyIterator) nextMany(hs uint32, buf []uint32) int {
 			bitset = bcmi.ptr.bitmap[base]
 			continue
 		}
-		t := bitset & -bitset
-		buf[n] = uint32(((base * 64) + bits.OnesCount64(t-1))) | hs
-		n = n + 1
-		bitset ^= t
+		if len(buf)-n >= 64 {
+			for bitset != 0 {
+				buf[n] = uint32((base*64)+bits.TrailingZeros64(bitset)) | hs
+				n++
+				bitset &= bitset - 1
+			}
+			continue
+		}
+		buf[n] = uint32((base*64)+bits.TrailingZeros64(bitset)) | hs
+		n++
+		bitset &= bitset - 1
 	}
 
 	bcmi.base = base
@@ -215,10 +222,17 @@ func (bcmi *bitmapContainerManyIterator) nextMany64(hs uint64, buf []uint64) int
 			bitset = bcmi.ptr.bitmap[base]
 			continue
 		}
-		t := bitset & -bitset
-		buf[n] = uint64(((base * 64) + bits.OnesCount64(t-1))) | hs
-		n = n + 1
-		bitset ^= t
+		if len(buf)-n >= 64 {
+			for bitset != 0 {
+				buf[n] = uint64((base*64)+bits.TrailingZeros64(bitset)) | hs
+				n++
+				bitset &= bitset - 1
+			}
+			continue
+		}
+		buf[n] = uint64((base*64)+bits.TrailingZeros64(bitset)) | hs
+		n++
+		bitset &= bitset - 1
 	}
 
 	bcmi.base = base
diff --git a/roaring64/manyiterator_bench_test.go b/roaring64/manyiterator_bench_test.go
new file mode 100644
index 00000000..ffb7c85d
--- /dev/null
+++ b/roaring64/manyiterator_bench_test.go
@@ -0,0 +1,49 @@
+package roaring64
+
+import "testing"
+
+const benchmarkRoaring64BatchCardinality = 1 << 15
+
+func benchmarkRoaring64BatchBitmap() *Bitmap {
+	values := make([]uint64, benchmarkRoaring64BatchCardinality)
+	for i := range values {
+		values[i] = uint64(i * 2)
+	}
+
+	bitmap := New()
+	bitmap.AddMany(values)
+	return bitmap
+}
+
+func BenchmarkRoaring64ToArray(b *testing.B) {
+	bitmap := benchmarkRoaring64BatchBitmap()
+	last := uint64((benchmarkRoaring64BatchCardinality - 1) * 2)
+
+	for b.Loop() {
+		values := bitmap.ToArray()
+		if len(values) != benchmarkRoaring64BatchCardinality || values[0] != 0 || values[len(values)-1] != last {
+			b.Fatal("unexpected bitmap contents")
+		}
+	}
+}
+
+func BenchmarkRoaring64ManyIterator(b *testing.B) {
+	bitmap := benchmarkRoaring64BatchBitmap()
+	values := make([]uint64, benchmarkRoaring64BatchCardinality)
+	last := uint64((benchmarkRoaring64BatchCardinality - 1) * 2)
+
+	for b.Loop() {
+		iterator := bitmap.ManyIterator()
+		n := 0
+		for n < len(values) {
+			count := iterator.NextMany(values[n:])
+			if count == 0 {
+				break
+			}
+			n += count
+		}
+		if n != len(values) || values[0] != 0 || values[n-1] != last {
+			b.Fatal("unexpected iterator contents")
+		}
+	}
+}