diff --git a/internal/handshake/crypto_setup.go b/internal/handshake/crypto_setup.go
index 1fe6c340..b0859d8b 100644
--- a/internal/handshake/crypto_setup.go
+++ b/internal/handshake/crypto_setup.go
@@ -223,7 +223,7 @@ func (h *cryptoSetup) ChangeConnectionID(id protocol.ConnectionID) error {
 	return nil
 }
 
-func (h *cryptoSetup) Received1RTTAck() {
+func (h *cryptoSetup) SetLargest1RTTAcked(_ protocol.PacketNumber) {
 	// drop initial keys
 	// TODO: do this earlier
 	if h.initialOpener != nil {
diff --git a/internal/handshake/interface.go b/internal/handshake/interface.go
index 07152c1f..55bc035d 100644
--- a/internal/handshake/interface.go
+++ b/internal/handshake/interface.go
@@ -71,7 +71,7 @@ type CryptoSetup interface {
 	ChangeConnectionID(protocol.ConnectionID) error
 
 	HandleMessage([]byte, protocol.EncryptionLevel) bool
-	Received1RTTAck()
+	SetLargest1RTTAcked(protocol.PacketNumber)
 	ConnectionState() tls.ConnectionState
 
 	GetInitialOpener() (LongHeaderOpener, error)
diff --git a/internal/mocks/crypto_setup.go b/internal/mocks/crypto_setup.go
index 77ed0bed..38449457 100644
--- a/internal/mocks/crypto_setup.go
+++ b/internal/mocks/crypto_setup.go
@@ -182,18 +182,6 @@ func (mr *MockCryptoSetupMockRecorder) HandleMessage(arg0, arg1 interface{}) *go
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "HandleMessage", reflect.TypeOf((*MockCryptoSetup)(nil).HandleMessage), arg0, arg1)
 }
 
-// Received1RTTAck mocks base method
-func (m *MockCryptoSetup) Received1RTTAck() {
-	m.ctrl.T.Helper()
-	m.ctrl.Call(m, "Received1RTTAck")
-}
-
-// Received1RTTAck indicates an expected call of Received1RTTAck
-func (mr *MockCryptoSetupMockRecorder) Received1RTTAck() *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Received1RTTAck", reflect.TypeOf((*MockCryptoSetup)(nil).Received1RTTAck))
-}
-
 // RunHandshake mocks base method
 func (m *MockCryptoSetup) RunHandshake() {
 	m.ctrl.T.Helper()
@@ -205,3 +193,15 @@ func (mr *MockCryptoSetupMockRecorder) RunHandshake() *gomock.Call {
 	mr.mock.ctrl.T.Helper()
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "RunHandshake", reflect.TypeOf((*MockCryptoSetup)(nil).RunHandshake))
 }
+
+// SetLargest1RTTAcked mocks base method
+func (m *MockCryptoSetup) SetLargest1RTTAcked(arg0 protocol.PacketNumber) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "SetLargest1RTTAcked", arg0)
+}
+
+// SetLargest1RTTAcked indicates an expected call of SetLargest1RTTAcked
+func (mr *MockCryptoSetupMockRecorder) SetLargest1RTTAcked(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "SetLargest1RTTAcked", reflect.TypeOf((*MockCryptoSetup)(nil).SetLargest1RTTAcked), arg0)
+}
diff --git a/session.go b/session.go
index d92f70c5..8b8939a2 100644
--- a/session.go
+++ b/session.go
@@ -50,7 +50,7 @@ type streamManager interface {
 type cryptoStreamHandler interface {
 	RunHandshake()
 	ChangeConnectionID(protocol.ConnectionID) error
-	Received1RTTAck()
+	SetLargest1RTTAcked(protocol.PacketNumber)
 	io.Closer
 	ConnectionState() tls.ConnectionState
 }
@@ -890,7 +890,7 @@ func (s *session) handleAckFrame(frame *wire.AckFrame, pn protocol.PacketNumber,
 	}
 	if encLevel == protocol.Encryption1RTT {
 		s.receivedPacketHandler.IgnoreBelow(s.sentPacketHandler.GetLowestPacketNotConfirmedAcked())
-		s.cryptoStreamHandler.Received1RTTAck()
+		s.cryptoStreamHandler.SetLargest1RTTAcked(frame.LargestAcked())
 	}
 	return nil
 }
diff --git a/session_test.go b/session_test.go
index 5399f938..03f2ebdf 100644
--- a/session_test.go
+++ b/session_test.go
@@ -163,7 +163,7 @@ var _ = Describe("Session", func() {
 			})
 
 			It("tells the ReceivedPacketHandler to ignore low ranges", func() {
-				cryptoSetup.EXPECT().Received1RTTAck()
+				cryptoSetup.EXPECT().SetLargest1RTTAcked(protocol.PacketNumber(3))
 				ack := &wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 2, Largest: 3}}}
 				sph := mockackhandler.NewMockSentPacketHandler(mockCtrl)
 				sph.EXPECT().ReceivedAck(gomock.Any(), gomock.Any(), gomock.Any(), gomock.Any())