diff --git a/ackhandler/retransmittable.go b/ackhandler/retransmittable.go
new file mode 100644
index 00000000..17437b8c
--- /dev/null
+++ b/ackhandler/retransmittable.go
@@ -0,0 +1,38 @@
+package ackhandler
+
+import (
+	"github.com/lucas-clemente/quic-go/frames"
+)
+
+// Returns a new slice with all non-retransmittable frames deleted.
+func stripNonRetransmittableFrames(fs []frames.Frame) []frames.Frame {
+	res := make([]frames.Frame, 0, len(fs))
+	for _, f := range fs {
+		if IsFrameRetransmittable(f) {
+			res = append(res, f)
+		}
+	}
+	return res
+}
+
+// IsFrameRetransmittable returns true if the frame should be retransmitted.
+func IsFrameRetransmittable(f frames.Frame) bool {
+	switch f.(type) {
+	case *frames.StopWaitingFrame:
+		return false
+	case *frames.AckFrame:
+		return false
+	default:
+		return true
+	}
+}
+
+// HasRetransmittableFrames returns true if at least one frame is retransmittable.
+func HasRetransmittableFrames(fs []frames.Frame) bool {
+	for _, f := range fs {
+		if IsFrameRetransmittable(f) {
+			return true
+		}
+	}
+	return false
+}
diff --git a/ackhandler/retransmittable_test.go b/ackhandler/retransmittable_test.go
new file mode 100644
index 00000000..4a5ea858
--- /dev/null
+++ b/ackhandler/retransmittable_test.go
@@ -0,0 +1,44 @@
+package ackhandler
+
+import (
+	"reflect"
+
+	"github.com/lucas-clemente/quic-go/frames"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("retransmittable frames", func() {
+	for fl, el := range map[frames.Frame]bool{
+		&frames.AckFrame{}:             false,
+		&frames.StopWaitingFrame{}:     false,
+		&frames.BlockedFrame{}:         true,
+		&frames.ConnectionCloseFrame{}: true,
+		&frames.GoawayFrame{}:          true,
+		&frames.PingFrame{}:            true,
+		&frames.RstStreamFrame{}:       true,
+		&frames.StreamFrame{}:          true,
+		&frames.WindowUpdateFrame{}:    true,
+	} {
+		f := fl
+		e := el
+		fName := reflect.ValueOf(f).Elem().Type().Name()
+
+		It("works for "+fName, func() {
+			Expect(IsFrameRetransmittable(f)).To(Equal(e))
+		})
+
+		It("stripping non-retransmittable frames works for "+fName, func() {
+			s := []frames.Frame{f}
+			if e {
+				Expect(stripNonRetransmittableFrames(s)).To(Equal([]frames.Frame{f}))
+			} else {
+				Expect(stripNonRetransmittableFrames(s)).To(BeEmpty())
+			}
+		})
+
+		It("HasRetransmittableFrames works for "+fName, func() {
+			Expect(HasRetransmittableFrames([]frames.Frame{f})).To(Equal(e))
+		})
+	}
+})
diff --git a/packet_unpacker.go b/packet_unpacker.go
index 30dee80a..c92e6a53 100644
--- a/packet_unpacker.go
+++ b/packet_unpacker.go
@@ -10,6 +10,11 @@ import (
 	"github.com/lucas-clemente/quic-go/qerr"
 )
 
+type unpackedPacket struct {
+	encryptionLevel protocol.EncryptionLevel
+	frames          []frames.Frame
+}
+
 type quicAEAD interface {
 	Open(dst, src []byte, packetNumber protocol.PacketNumber, associatedData []byte) ([]byte, protocol.EncryptionLevel, error)
 }
diff --git a/session.go b/session.go
index 6e187a7e..0bebe993 100644
--- a/session.go
+++ b/session.go
@@ -405,7 +405,8 @@ func (s *session) handlePacketImpl(p *receivedPacket) error {
 	// Only do this after decrypting, so we are sure the packet is not attacker-controlled
 	s.largestRcvdPacketNumber = utils.MaxPacketNumber(s.largestRcvdPacketNumber, hdr.PacketNumber)
 
-	if err = s.receivedPacketHandler.ReceivedPacket(hdr.PacketNumber, packet.IsRetransmittable()); err != nil {
+	isRetransmittable := ackhandler.HasRetransmittableFrames(packet.frames)
+	if err = s.receivedPacketHandler.ReceivedPacket(hdr.PacketNumber, isRetransmittable); err != nil {
 		return err
 	}
 
diff --git a/unpacked_packet.go b/unpacked_packet.go
deleted file mode 100644
index 0636b8f1..00000000
--- a/unpacked_packet.go
+++ /dev/null
@@ -1,31 +0,0 @@
-package quic
-
-import (
-	"github.com/lucas-clemente/quic-go/frames"
-	"github.com/lucas-clemente/quic-go/protocol"
-)
-
-type unpackedPacket struct {
-	encryptionLevel protocol.EncryptionLevel
-	frames          []frames.Frame
-}
-
-func (u *unpackedPacket) IsRetransmittable() bool {
-	for _, f := range u.frames {
-		switch f.(type) {
-		case *frames.StreamFrame:
-			return true
-		case *frames.RstStreamFrame:
-			return true
-		case *frames.WindowUpdateFrame:
-			return true
-		case *frames.BlockedFrame:
-			return true
-		case *frames.PingFrame:
-			return true
-		case *frames.GoawayFrame:
-			return true
-		}
-	}
-	return false
-}
diff --git a/unpacked_packet_test.go b/unpacked_packet_test.go
deleted file mode 100644
index 82112a26..00000000
--- a/unpacked_packet_test.go
+++ /dev/null
@@ -1,46 +0,0 @@
-package quic
-
-import (
-	"github.com/lucas-clemente/quic-go/frames"
-	. "github.com/onsi/ginkgo"
-	. "github.com/onsi/gomega"
-)
-
-var _ = Describe("Unpacked packet", func() {
-	var packet *unpackedPacket
-	BeforeEach(func() {
-		packet = &unpackedPacket{}
-	})
-
-	It("says that an empty packet is not retransmittable", func() {
-		Expect(packet.IsRetransmittable()).To(BeFalse())
-	})
-
-	It("detects the frame types", func() {
-		packet.frames = []frames.Frame{&frames.AckFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeFalse())
-		packet.frames = []frames.Frame{&frames.BlockedFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeTrue())
-		packet.frames = []frames.Frame{&frames.GoawayFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeTrue())
-		packet.frames = []frames.Frame{&frames.PingFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeTrue())
-		packet.frames = []frames.Frame{&frames.StreamFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeTrue())
-		packet.frames = []frames.Frame{&frames.RstStreamFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeTrue())
-		packet.frames = []frames.Frame{&frames.StopWaitingFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeFalse())
-		packet.frames = []frames.Frame{&frames.WindowUpdateFrame{}}
-		Expect(packet.IsRetransmittable()).To(BeTrue())
-	})
-
-	It("says that a packet is retransmittable if it contains one retransmittable frame", func() {
-		packet.frames = []frames.Frame{
-			&frames.AckFrame{},
-			&frames.WindowUpdateFrame{},
-			&frames.StopWaitingFrame{},
-		}
-		Expect(packet.IsRetransmittable()).To(BeTrue())
-	})
-})