diff --git a/frames/ack_frame_new.go b/frames/ack_frame_new.go
index 7e211b80..c52cf542 100644
--- a/frames/ack_frame_new.go
+++ b/frames/ack_frame_new.go
@@ -179,3 +179,11 @@ func (f *AckFrameNew) HasNACK() bool {
 	}
 	return false
 }
+
+// GetHighestInOrderPacketNumber gets the highest in order packet number that is confirmed by this ACK
+func (f *AckFrameNew) GetHighestInOrderPacketNumber() protocol.PacketNumber {
+	if f.HasNACK() {
+		panic("NACKs not yet implemented")
+	}
+	return f.LargestObserved
+}
diff --git a/frames/ack_frame_new_test.go b/frames/ack_frame_new_test.go
index 9564cc17..98d0d2a9 100644
--- a/frames/ack_frame_new_test.go
+++ b/frames/ack_frame_new_test.go
@@ -62,6 +62,16 @@ var _ = Describe("AckFrame", func() {
 		})
 	})
 
+	Context("highest in order packet number", func() {
+		It("gets the hightest in order packet number for a simple ACK", func() {
+			frame := &AckFrameNew{
+				LargestObserved: 0x1337,
+			}
+			Expect(frame.GetHighestInOrderPacketNumber()).To(Equal(protocol.PacketNumber(0x1337)))
+		})
+
+	})
+
 	Context("self-consistency checks", func() {
 		var b *bytes.Buffer
 		BeforeEach(func() {