diff --git a/ackhandler/received_packet_handler.go b/ackhandler/received_packet_handler.go
index b54e15a02..97410f375 100644
--- a/ackhandler/received_packet_handler.go
+++ b/ackhandler/received_packet_handler.go
@@ -1,15 +1,12 @@
 package ackhandler
 
 import (
-	"errors"
 	"time"
 
 	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/wire"
 )
 
-var errInvalidPacketNumber = errors.New("ReceivedPacketHandler: Invalid packet number")
-
 type receivedPacketHandler struct {
 	largestObserved             protocol.PacketNumber
 	ignoreBelow                 protocol.PacketNumber
@@ -38,10 +35,6 @@ func NewReceivedPacketHandler(version protocol.VersionNumber) ReceivedPacketHand
 }
 
 func (h *receivedPacketHandler) ReceivedPacket(packetNumber protocol.PacketNumber, shouldInstigateAck bool) error {
-	if packetNumber == 0 {
-		return errInvalidPacketNumber
-	}
-
 	if packetNumber > h.largestObserved {
 		h.largestObserved = packetNumber
 		h.largestObservedReceivedTime = time.Now()
diff --git a/ackhandler/received_packet_handler_test.go b/ackhandler/received_packet_handler_test.go
index c1d7ecd59..4a87c72d9 100644
--- a/ackhandler/received_packet_handler_test.go
+++ b/ackhandler/received_packet_handler_test.go
@@ -29,11 +29,6 @@ var _ = Describe("receivedPacketHandler", func() {
 			Expect(err).ToNot(HaveOccurred())
 		})
 
-		It("rejects packets with packet number 0", func() {
-			err := handler.ReceivedPacket(protocol.PacketNumber(0), true)
-			Expect(err).To(MatchError(errInvalidPacketNumber))
-		})
-
 		It("saves the time when each packet arrived", func() {
 			err := handler.ReceivedPacket(protocol.PacketNumber(3), true)
 			Expect(err).ToNot(HaveOccurred())
@@ -91,14 +86,11 @@ var _ = Describe("receivedPacketHandler", func() {
 				Expect(handler.GetAlarmTimeout()).To(BeZero())
 			})
 
-			It("doesn't queue an ACK for non-retransmittable packets", func() {
-				receiveAndAck10Packets()
-				handler.version = protocol.Version39
-				for i := 11; i < 1000; i++ {
-					err := handler.ReceivedPacket(protocol.PacketNumber(i), false)
-					Expect(err).ToNot(HaveOccurred())
-					Expect(handler.ackQueued).To(BeFalse())
-				}
+			It("works with packet number 0", func() {
+				err := handler.ReceivedPacket(0, false)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(handler.ackQueued).To(BeTrue())
+				Expect(handler.GetAlarmTimeout()).To(BeZero())
 			})
 
 			It("queues an ACK for every second retransmittable packet, if they are arriving fast", func() {
@@ -173,6 +165,16 @@ var _ = Describe("receivedPacketHandler", func() {
 				Expect(ack.AckRanges).To(BeEmpty())
 			})
 
+			It("generates an ACK for packet number 0", func() {
+				err := handler.ReceivedPacket(0, true)
+				Expect(err).ToNot(HaveOccurred())
+				ack := handler.GetAckFrame()
+				Expect(ack).ToNot(BeNil())
+				Expect(ack.LargestAcked).To(Equal(protocol.PacketNumber(0)))
+				Expect(ack.LowestAcked).To(Equal(protocol.PacketNumber(0)))
+				Expect(ack.AckRanges).To(BeEmpty())
+			})
+
 			It("saves the last sent ACK", func() {
 				err := handler.ReceivedPacket(1, true)
 				Expect(err).ToNot(HaveOccurred())
@@ -196,9 +198,27 @@ var _ = Describe("receivedPacketHandler", func() {
 				Expect(ack).ToNot(BeNil())
 				Expect(ack.LargestAcked).To(Equal(protocol.PacketNumber(4)))
 				Expect(ack.LowestAcked).To(Equal(protocol.PacketNumber(1)))
-				Expect(ack.AckRanges).To(HaveLen(2))
-				Expect(ack.AckRanges[0]).To(Equal(wire.AckRange{First: 4, Last: 4}))
-				Expect(ack.AckRanges[1]).To(Equal(wire.AckRange{First: 1, Last: 1}))
+				Expect(ack.AckRanges).To(Equal([]wire.AckRange{
+					wire.AckRange{First: 4, Last: 4},
+					wire.AckRange{First: 1, Last: 1},
+				}))
+			})
+
+			It("generates an ACK for packet number 0 and other packets", func() {
+				err := handler.ReceivedPacket(0, true)
+				Expect(err).ToNot(HaveOccurred())
+				err = handler.ReceivedPacket(1, true)
+				Expect(err).ToNot(HaveOccurred())
+				err = handler.ReceivedPacket(3, true)
+				Expect(err).ToNot(HaveOccurred())
+				ack := handler.GetAckFrame()
+				Expect(ack).ToNot(BeNil())
+				Expect(ack.LargestAcked).To(Equal(protocol.PacketNumber(3)))
+				Expect(ack.LowestAcked).To(Equal(protocol.PacketNumber(0)))
+				Expect(ack.AckRanges).To(Equal([]wire.AckRange{
+					wire.AckRange{First: 3, Last: 3},
+					wire.AckRange{First: 0, Last: 1},
+				}))
 			})
 
 			It("accepts packets below the lower limit", func() {