diff --git a/internal/mocks/gen.go b/internal/mocks/gen.go
index 79d3e2fe5..33df5c995 100644
--- a/internal/mocks/gen.go
+++ b/internal/mocks/gen.go
@@ -4,6 +4,7 @@ package mocks
 //go:generate sh -c "./mockgen_internal.sh mocks tls_extension_handler.go github.com/lucas-clemente/quic-go/internal/handshake TLSExtensionHandler"
 //go:generate sh -c "./mockgen_internal.sh mocks stream_flow_controller.go github.com/lucas-clemente/quic-go/internal/flowcontrol StreamFlowController"
 //go:generate sh -c "./mockgen_internal.sh mocks sent_packet_handler.go github.com/lucas-clemente/quic-go/ackhandler SentPacketHandler"
+//go:generate sh -c "./mockgen_internal.sh mocks received_packet_handler.go github.com/lucas-clemente/quic-go/ackhandler ReceivedPacketHandler"
 //go:generate sh -c "./mockgen_internal.sh mocks connection_flow_controller.go github.com/lucas-clemente/quic-go/internal/flowcontrol ConnectionFlowController"
 //go:generate sh -c "./mockgen_internal.sh mockcrypto crypto/aead.go github.com/lucas-clemente/quic-go/internal/crypto AEAD"
 //go:generate sh -c "./mockgen_stream.sh mocks stream.go github.com/lucas-clemente/quic-go StreamI"
diff --git a/internal/mocks/received_packet_handler.go b/internal/mocks/received_packet_handler.go
new file mode 100644
index 000000000..a47424c79
--- /dev/null
+++ b/internal/mocks/received_packet_handler.go
@@ -0,0 +1,82 @@
+// Code generated by MockGen. DO NOT EDIT.
+// Source: github.com/lucas-clemente/quic-go/ackhandler (interfaces: ReceivedPacketHandler)
+
+package mocks
+
+import (
+	reflect "reflect"
+	time "time"
+
+	gomock "github.com/golang/mock/gomock"
+	protocol "github.com/lucas-clemente/quic-go/internal/protocol"
+	wire "github.com/lucas-clemente/quic-go/internal/wire"
+)
+
+// MockReceivedPacketHandler is a mock of ReceivedPacketHandler interface
+type MockReceivedPacketHandler struct {
+	ctrl     *gomock.Controller
+	recorder *MockReceivedPacketHandlerMockRecorder
+}
+
+// MockReceivedPacketHandlerMockRecorder is the mock recorder for MockReceivedPacketHandler
+type MockReceivedPacketHandlerMockRecorder struct {
+	mock *MockReceivedPacketHandler
+}
+
+// NewMockReceivedPacketHandler creates a new mock instance
+func NewMockReceivedPacketHandler(ctrl *gomock.Controller) *MockReceivedPacketHandler {
+	mock := &MockReceivedPacketHandler{ctrl: ctrl}
+	mock.recorder = &MockReceivedPacketHandlerMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use
+func (_m *MockReceivedPacketHandler) EXPECT() *MockReceivedPacketHandlerMockRecorder {
+	return _m.recorder
+}
+
+// GetAckFrame mocks base method
+func (_m *MockReceivedPacketHandler) GetAckFrame() *wire.AckFrame {
+	ret := _m.ctrl.Call(_m, "GetAckFrame")
+	ret0, _ := ret[0].(*wire.AckFrame)
+	return ret0
+}
+
+// GetAckFrame indicates an expected call of GetAckFrame
+func (_mr *MockReceivedPacketHandlerMockRecorder) GetAckFrame() *gomock.Call {
+	return _mr.mock.ctrl.RecordCallWithMethodType(_mr.mock, "GetAckFrame", reflect.TypeOf((*MockReceivedPacketHandler)(nil).GetAckFrame))
+}
+
+// GetAlarmTimeout mocks base method
+func (_m *MockReceivedPacketHandler) GetAlarmTimeout() time.Time {
+	ret := _m.ctrl.Call(_m, "GetAlarmTimeout")
+	ret0, _ := ret[0].(time.Time)
+	return ret0
+}
+
+// GetAlarmTimeout indicates an expected call of GetAlarmTimeout
+func (_mr *MockReceivedPacketHandlerMockRecorder) GetAlarmTimeout() *gomock.Call {
+	return _mr.mock.ctrl.RecordCallWithMethodType(_mr.mock, "GetAlarmTimeout", reflect.TypeOf((*MockReceivedPacketHandler)(nil).GetAlarmTimeout))
+}
+
+// IgnoreBelow mocks base method
+func (_m *MockReceivedPacketHandler) IgnoreBelow(_param0 protocol.PacketNumber) {
+	_m.ctrl.Call(_m, "IgnoreBelow", _param0)
+}
+
+// IgnoreBelow indicates an expected call of IgnoreBelow
+func (_mr *MockReceivedPacketHandlerMockRecorder) IgnoreBelow(arg0 interface{}) *gomock.Call {
+	return _mr.mock.ctrl.RecordCallWithMethodType(_mr.mock, "IgnoreBelow", reflect.TypeOf((*MockReceivedPacketHandler)(nil).IgnoreBelow), arg0)
+}
+
+// ReceivedPacket mocks base method
+func (_m *MockReceivedPacketHandler) ReceivedPacket(_param0 protocol.PacketNumber, _param1 bool) error {
+	ret := _m.ctrl.Call(_m, "ReceivedPacket", _param0, _param1)
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// ReceivedPacket indicates an expected call of ReceivedPacket
+func (_mr *MockReceivedPacketHandlerMockRecorder) ReceivedPacket(arg0, arg1 interface{}) *gomock.Call {
+	return _mr.mock.ctrl.RecordCallWithMethodType(_mr.mock, "ReceivedPacket", reflect.TypeOf((*MockReceivedPacketHandler)(nil).ReceivedPacket), arg0, arg1)
+}
diff --git a/session_test.go b/session_test.go
index 80462e090..ba69137e2 100644
--- a/session_test.go
+++ b/session_test.go
@@ -70,26 +70,6 @@ func (m *mockUnpacker) Unpack(headerBinary []byte, hdr *wire.Header, data []byte
 	}, nil
 }
 
-type mockReceivedPacketHandler struct {
-	nextAckFrame *wire.AckFrame
-	ackAlarm     time.Time
-}
-
-func (m *mockReceivedPacketHandler) GetAckFrame() *wire.AckFrame {
-	f := m.nextAckFrame
-	m.nextAckFrame = nil
-	return f
-}
-func (m *mockReceivedPacketHandler) ReceivedPacket(packetNumber protocol.PacketNumber, shouldInstigateAck bool) error {
-	panic("not implemented")
-}
-func (m *mockReceivedPacketHandler) IgnoreBelow(protocol.PacketNumber) {
-	panic("not implemented")
-}
-func (m *mockReceivedPacketHandler) GetAlarmTimeout() time.Time { return m.ackAlarm }
-
-var _ ackhandler.ReceivedPacketHandler = &mockReceivedPacketHandler{}
-
 func areSessionsRunning() bool {
 	var b bytes.Buffer
 	pprof.Lookup("goroutine").WriteTo(&b, 1)
@@ -1000,10 +980,14 @@ var _ = Describe("Session", func() {
 		})
 
 		It("sets the timer to the ack timer", func() {
-			rph := &mockReceivedPacketHandler{ackAlarm: time.Now().Add(10 * time.Millisecond)}
-			rph.nextAckFrame = &wire.AckFrame{LargestAcked: 0x1337}
+			rph := mocks.NewMockReceivedPacketHandler(mockCtrl)
+			rph.EXPECT().GetAckFrame().Return(&wire.AckFrame{LargestAcked: 0x1337})
+			rph.EXPECT().GetAlarmTimeout().Return(time.Now().Add(10 * time.Millisecond)).MinTimes(1)
 			sess.receivedPacketHandler = rph
-			go sess.run()
+			go func() {
+				defer GinkgoRecover()
+				sess.run()
+			}()
 			defer sess.Close(nil)
 			time.Sleep(10 * time.Millisecond)
 			Eventually(func() int { return len(mconn.written) }).ShouldNot(BeZero())