diff --git a/frames/ack_frame.go b/frames/ack_frame.go
index 2e91babb6..87c8cb5c2 100644
--- a/frames/ack_frame.go
+++ b/frames/ack_frame.go
@@ -21,8 +21,10 @@ var (
 	errInconsistentAckLowestAcked  = errors.New("internal inconsistency: LowestAcked does not match ACK ranges")
 )
 
-// An AckFrame is a ACK frame in QUIC c34
+// An AckFrame is an ACK frame in QUIC
 type AckFrame struct {
+	AckFrameLegacy *AckFrameLegacy
+
 	LargestAcked protocol.PacketNumber
 	LowestAcked  protocol.PacketNumber
 	AckRanges    []AckRange // has to be ordered. The ACK range with the highest FirstPacketNumber goes first, the ACK range with the lowest FirstPacketNumber goes last
@@ -35,6 +37,15 @@ type AckFrame struct {
 func ParseAckFrame(r *bytes.Reader, version protocol.VersionNumber) (*AckFrame, error) {
 	frame := &AckFrame{}
 
+	if version != protocol.VersionWhatever && version <= protocol.Version33 {
+		var err error
+		frame.AckFrameLegacy, err = ParseAckFrameLegacy(r, version)
+		if err != nil {
+			return nil, err
+		}
+		return frame, nil
+	}
+
 	typeByte, err := r.ReadByte()
 	if err != nil {
 		return nil, err
@@ -187,6 +198,10 @@ func ParseAckFrame(r *bytes.Reader, version protocol.VersionNumber) (*AckFrame,
 
 // Write writes an ACK frame.
 func (f *AckFrame) Write(b *bytes.Buffer, version protocol.VersionNumber) error {
+	if f.AckFrameLegacy != nil {
+		return f.AckFrameLegacy.Write(b, version)
+	}
+
 	largestAckedLen := protocol.GetPacketNumberLength(f.LargestAcked)
 
 	typeByte := uint8(0x40)
@@ -327,6 +342,10 @@ func (f *AckFrame) Write(b *bytes.Buffer, version protocol.VersionNumber) error
 
 // MinLength of a written frame
 func (f *AckFrame) MinLength(version protocol.VersionNumber) (protocol.ByteCount, error) {
+	if f.AckFrameLegacy != nil {
+		return f.AckFrameLegacy.MinLength(version)
+	}
+
 	var length protocol.ByteCount
 	length = 1 + 2 + 1 // 1 TypeByte, 2 ACK delay time, 1 Num Timestamp
 	length += protocol.ByteCount(protocol.GetPacketNumberLength(f.LargestAcked))
@@ -346,6 +365,10 @@ func (f *AckFrame) MinLength(version protocol.VersionNumber) (protocol.ByteCount
 
 // HasMissingRanges returns if this frame reports any missing packets
 func (f *AckFrame) HasMissingRanges() bool {
+	if f.AckFrameLegacy != nil {
+		panic("HasMissingRanges() should not be called on an AckFrameLegacy")
+	}
+
 	if len(f.AckRanges) > 0 {
 		return true
 	}
diff --git a/frames/ack_frame_test.go b/frames/ack_frame_test.go
index 94a1c1352..e618d492e 100644
--- a/frames/ack_frame_test.go
+++ b/frames/ack_frame_test.go
@@ -832,4 +832,46 @@ var _ = Describe("AckFrame", func() {
 			Expect(ack.validateAckRanges()).To(BeTrue())
 		})
 	})
+
+	Context("Legacy AckFrame wrapping", func() {
+		It("parses a ACK frame", func() {
+			b := bytes.NewReader([]byte{0x40, 0xA4, 0x03, 0x23, 0x45, 0x01, 0x02, 0xFF, 0xEE, 0xDD, 0xCC})
+			frame, err := ParseAckFrame(b, protocol.Version32)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(frame.AckFrameLegacy).ToNot(BeNil())
+			Expect(frame.AckFrameLegacy.Entropy).To(Equal(byte(0xA4)))
+			Expect(frame.AckFrameLegacy.LargestObserved).To(Equal(protocol.PacketNumber(0x03)))
+			Expect(frame.LargestAcked).To(BeZero())
+			Expect(frame.LowestAcked).To(BeZero())
+			Expect(b.Len()).To(Equal(0))
+		})
+
+		It("writes an ACK frame", func() {
+			b1 := &bytes.Buffer{}
+			b2 := &bytes.Buffer{}
+			ackLegacy := &AckFrameLegacy{
+				Entropy:         2,
+				LargestObserved: 1,
+			}
+			frame := AckFrame{
+				AckFrameLegacy: ackLegacy,
+			}
+			err := frame.Write(b1, protocol.Version32)
+			Expect(err).ToNot(HaveOccurred())
+			err = ackLegacy.Write(b2, protocol.Version32)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(b1.Bytes()).To(Equal(b2.Bytes()))
+		})
+
+		It("determines the minLength", func() {
+			ackLegacy := &AckFrameLegacy{
+				Entropy:         2,
+				LargestObserved: 1,
+			}
+			ack := AckFrame{AckFrameLegacy: ackLegacy}
+			minLengthLegacy, _ := ackLegacy.MinLength(0)
+			minLength, _ := ack.MinLength(0)
+			Expect(minLength).To(Equal(minLengthLegacy))
+		})
+	})
 })