diff --git a/frames/ack_frame.go b/frames/ack_frame.go
index b68b4482..07cbfe13 100644
--- a/frames/ack_frame.go
+++ b/frames/ack_frame.go
@@ -83,7 +83,7 @@ func ParseAckFrame(r *bytes.Reader, version protocol.VersionNumber) (*AckFrame,
 	if err != nil {
 		return nil, err
 	}
-	if ackBlockLength < 1 {
+	if frame.LargestAcked > 0 && ackBlockLength < 1 {
 		return nil, ErrInvalidFirstAckRange
 	}
 
@@ -141,7 +141,11 @@ func ParseAckFrame(r *bytes.Reader, version protocol.VersionNumber) (*AckFrame,
 
 		frame.LowestAcked = frame.AckRanges[len(frame.AckRanges)-1].FirstPacketNumber
 	} else {
-		frame.LowestAcked = protocol.PacketNumber(largestAcked + 1 - ackBlockLength)
+		if frame.LargestAcked == 0 {
+			frame.LowestAcked = 0
+		} else {
+			frame.LowestAcked = protocol.PacketNumber(largestAcked + 1 - ackBlockLength)
+		}
 	}
 
 	if !frame.validateAckRanges() {
diff --git a/frames/ack_frame_test.go b/frames/ack_frame_test.go
index 1c86ff81..1928179e 100644
--- a/frames/ack_frame_test.go
+++ b/frames/ack_frame_test.go
@@ -29,6 +29,16 @@ var _ = Describe("AckFrame", func() {
 			Expect(frame.LargestAcked).To(Equal(protocol.PacketNumber(3)))
 		})
 
+		It("parses a frame where the largest acked is 0", func() {
+			b := bytes.NewReader([]byte{0x40, 0x0, 0xff, 0xff, 0x0, 0x0})
+			frame, err := ParseAckFrame(b, 0)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(frame.LargestAcked).To(Equal(protocol.PacketNumber(0)))
+			Expect(frame.LowestAcked).To(Equal(protocol.PacketNumber(0)))
+			Expect(frame.HasMissingRanges()).To(BeFalse())
+			Expect(b.Len()).To(BeZero())
+		})
+
 		It("parses a frame with a 48 bit packet number", func() {
 			b := bytes.NewReader([]byte{0x4c, 0x37, 0x13, 0xad, 0xfb, 0xca, 0xde, 0x0, 0x0, 0x5, 0x1, 0, 0, 0, 0, 0})
 			frame, err := ParseAckFrame(b, 0)