diff --git a/internal/ackhandler/interfaces.go b/internal/ackhandler/interfaces.go
index a2249b351..d0bce26e7 100644
--- a/internal/ackhandler/interfaces.go
+++ b/internal/ackhandler/interfaces.go
@@ -27,6 +27,7 @@ type SentPacketHandler interface {
 	// Before sending any packet, SendingAllowed() must be called to learn if we can actually send it.
 	ShouldSendNumPackets() int
 
+	// only to be called once the handshake is complete
 	GetLowestPacketNotConfirmedAcked() protocol.PacketNumber
 	DequeuePacketForRetransmission() *Packet
 	DequeueProbePacket() (*Packet, error)
diff --git a/session.go b/session.go
index 3021e782d..69d2cf7a2 100644
--- a/session.go
+++ b/session.go
@@ -726,7 +726,9 @@ func (s *session) handleAckFrame(frame *wire.AckFrame, pn protocol.PacketNumber,
 	if err := s.sentPacketHandler.ReceivedAck(frame, pn, encLevel, s.lastNetworkActivityTime); err != nil {
 		return err
 	}
-	s.receivedPacketHandler.IgnoreBelow(s.sentPacketHandler.GetLowestPacketNotConfirmedAcked())
+	if encLevel == protocol.Encryption1RTT {
+		s.receivedPacketHandler.IgnoreBelow(s.sentPacketHandler.GetLowestPacketNotConfirmedAcked())
+	}
 	return nil
 }
 
diff --git a/session_test.go b/session_test.go
index d7a70b9a9..f0bb07963 100644
--- a/session_test.go
+++ b/session_test.go
@@ -159,7 +159,6 @@ var _ = Describe("Session", func() {
 				f := &wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 2, Largest: 3}}}
 				sph := mockackhandler.NewMockSentPacketHandler(mockCtrl)
 				sph.EXPECT().ReceivedAck(f, protocol.PacketNumber(42), protocol.EncryptionHandshake, gomock.Any())
-				sph.EXPECT().GetLowestPacketNotConfirmedAcked()
 				sess.sentPacketHandler = sph
 				err := sess.handleAckFrame(f, 42, protocol.EncryptionHandshake)
 				Expect(err).ToNot(HaveOccurred())
@@ -174,7 +173,7 @@ var _ = Describe("Session", func() {
 				rph := mockackhandler.NewMockReceivedPacketHandler(mockCtrl)
 				rph.EXPECT().IgnoreBelow(protocol.PacketNumber(0x42))
 				sess.receivedPacketHandler = rph
-				Expect(sess.handleAckFrame(ack, 0, protocol.EncryptionInitial)).To(Succeed())
+				Expect(sess.handleAckFrame(ack, 0, protocol.Encryption1RTT)).To(Succeed())
 			})
 		})