diff --git a/.gitattributes b/.gitattributes
index 2ee232be3..1c25f9553 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -6,4 +6,3 @@ vendor/**   -text=auto
 
 # Diffs on these files are meaningless
 *.svg           -diff
-*.pb.go         -diff
diff --git a/lib/protocol/bep.pb.go b/lib/protocol/bep.pb.go
index 3efd29fa7..53f3f6e7e 100644
--- a/lib/protocol/bep.pb.go
+++ b/lib/protocol/bep.pb.go
@@ -383,7 +383,7 @@ type FileDownloadProgressUpdate struct {
 	UpdateType   FileDownloadProgressUpdateType `protobuf:"varint,1,opt,name=update_type,json=updateType,proto3,enum=protocol.FileDownloadProgressUpdateType" json:"update_type,omitempty"`
 	Name         string                         `protobuf:"bytes,2,opt,name=name,proto3" json:"name,omitempty"`
 	Version      Vector                         `protobuf:"bytes,3,opt,name=version" json:"version"`
-	BlockIndexes []int32                        `protobuf:"varint,4,rep,packed,name=block_indexes,json=blockIndexes" json:"block_indexes,omitempty"`
+	BlockIndexes []int32                        `protobuf:"varint,4,rep,name=block_indexes,json=blockIndexes" json:"block_indexes,omitempty"`
 }
 
 func (m *FileDownloadProgressUpdate) Reset()                    { *m = FileDownloadProgressUpdate{} }
@@ -1163,22 +1163,11 @@ func (m *FileDownloadProgressUpdate) MarshalTo(data []byte) (int, error) {
 	}
 	i += n3
 	if len(m.BlockIndexes) > 0 {
-		data5 := make([]byte, len(m.BlockIndexes)*10)
-		var j4 int
-		for _, num1 := range m.BlockIndexes {
-			num := uint64(num1)
-			for num >= 1<<7 {
-				data5[j4] = uint8(uint64(num)&0x7f | 0x80)
-				num >>= 7
-				j4++
-			}
-			data5[j4] = uint8(num)
-			j4++
+		for _, num := range m.BlockIndexes {
+			data[i] = 0x20
+			i++
+			i = encodeVarintBep(data, i, uint64(num))
 		}
-		data[i] = 0x22
-		i++
-		i = encodeVarintBep(data, i, uint64(j4))
-		i += copy(data[i:], data5[:j4])
 	}
 	return i, nil
 }
@@ -1568,11 +1557,9 @@ func (m *FileDownloadProgressUpdate) ProtoSize() (n int) {
 	l = m.Version.ProtoSize()
 	n += 1 + l + sovBep(uint64(l))
 	if len(m.BlockIndexes) > 0 {
-		l = 0
 		for _, e := range m.BlockIndexes {
-			l += sovBep(uint64(e))
+			n += 1 + sovBep(uint64(e))
 		}
-		n += 1 + sovBep(uint64(l)) + l
 	}
 	return n
 }
diff --git a/lib/protocol/protocol_test.go b/lib/protocol/protocol_test.go
index 778f63494..dc2e35367 100644
--- a/lib/protocol/protocol_test.go
+++ b/lib/protocol/protocol_test.go
@@ -13,6 +13,8 @@ import (
 	"testing/quick"
 	"time"
 
+	"encoding/hex"
+
 	"github.com/syncthing/syncthing/lib/rand"
 )
 
@@ -179,6 +181,37 @@ func TestMarshalCloseMessage(t *testing.T) {
 	}
 }
 
+func TestMarshalFDPU(t *testing.T) {
+	if testing.Short() {
+		quickCfg.MaxCount = 10
+	}
+
+	f := func(m1 FileDownloadProgressUpdate) bool {
+		if len(m1.Version.Counters) == 0 {
+			m1.Version.Counters = nil
+		}
+		return testMarshal(t, "close", &m1, &FileDownloadProgressUpdate{})
+	}
+
+	if err := quick.Check(f, quickCfg); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestUnmarshalFDPUv16v17(t *testing.T) {
+	var fdpu FileDownloadProgressUpdate
+
+	m0, _ := hex.DecodeString("08cda1e2e3011278f3918787f3b89b8af2958887f0aa9389f3a08588f3aa8f96f39aa8a5f48b9188f19286a0f3848da4f3aba799f3beb489f0a285b9f487b684f2a3bda2f48598b4f2938a89f2a28badf187a0a2f2aebdbdf4849494f4808fbbf2b3a2adf2bb95bff0a6ada4f198ab9af29a9c8bf1abb793f3baabb2f188a6ba1a0020bb9390f60220f6d9e42220b0c7e2b2fdffffffff0120fdb2dfcdfbffffffff0120cedab1d50120bd8784c0feffffffff0120ace99591fdffffffff0120eed7d09af9ffffffff01")
+	if err := fdpu.Unmarshal(m0); err != nil {
+		t.Fatal("Unmarshalling message from v0.14.16:", err)
+	}
+
+	m1, _ := hex.DecodeString("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")
+	if err := fdpu.Unmarshal(m1); err != nil {
+		t.Fatal("Unmarshalling message from v0.14.16:", err)
+	}
+}
+
 func testMarshal(t *testing.T, prefix string, m1, m2 message) bool {
 	buf, err := m1.Marshal()
 	if err != nil {
@@ -194,7 +227,7 @@ func testMarshal(t *testing.T, prefix string, m1, m2 message) bool {
 	bs2, _ := json.MarshalIndent(m2, "", "  ")
 	if !bytes.Equal(bs1, bs2) {
 		ioutil.WriteFile(prefix+"-1.txt", bs1, 0644)
-		ioutil.WriteFile(prefix+"-2.txt", bs1, 0644)
+		ioutil.WriteFile(prefix+"-2.txt", bs2, 0644)
 		return false
 	}