diff --git a/protocol/marshal.go b/protocol/marshal.go
index 728b81845..c1bce9270 100644
--- a/protocol/marshal.go
+++ b/protocol/marshal.go
@@ -3,6 +3,7 @@ package protocol
 import (
 	"errors"
 	"io"
+	"sync/atomic"
 
 	"github.com/calmh/syncthing/buffers"
 )
@@ -19,7 +20,7 @@ var padBytes = []byte{0, 0, 0}
 
 type marshalWriter struct {
 	w   io.Writer
-	tot int
+	tot uint64
 	err error
 	b   [8]byte
 }
@@ -51,7 +52,7 @@ func (w *marshalWriter) writeBytes(bs []byte) {
 	if p := pad(len(bs)); w.err == nil && p > 0 {
 		_, w.err = w.w.Write(padBytes[:p])
 	}
-	w.tot += len(bs) + pad(len(bs))
+	atomic.AddUint64(&w.tot, uint64(len(bs)+pad(len(bs))))
 }
 
 func (w *marshalWriter) writeUint32(v uint32) {
@@ -63,7 +64,7 @@ func (w *marshalWriter) writeUint32(v uint32) {
 	w.b[2] = byte(v >> 8)
 	w.b[3] = byte(v)
 	_, w.err = w.w.Write(w.b[:4])
-	w.tot += 4
+	atomic.AddUint64(&w.tot, 4)
 }
 
 func (w *marshalWriter) writeUint64(v uint64) {
@@ -79,12 +80,16 @@ func (w *marshalWriter) writeUint64(v uint64) {
 	w.b[6] = byte(v >> 8)
 	w.b[7] = byte(v)
 	_, w.err = w.w.Write(w.b[:8])
-	w.tot += 8
+	atomic.AddUint64(&w.tot, 8)
+}
+
+func (w *marshalWriter) getTot() uint64 {
+	return atomic.LoadUint64(&w.tot)
 }
 
 type marshalReader struct {
 	r   io.Reader
-	tot int
+	tot uint64
 	err error
 	b   [8]byte
 }
@@ -109,7 +114,7 @@ func (r *marshalReader) readBytes() []byte {
 	}
 	b := buffers.Get(l + pad(l))
 	_, r.err = io.ReadFull(r.r, b)
-	r.tot += int(l + pad(l))
+	atomic.AddUint64(&r.tot, uint64(l+pad(l)))
 	return b[:l]
 }
 
@@ -118,7 +123,7 @@ func (r *marshalReader) readUint32() uint32 {
 		return 0
 	}
 	_, r.err = io.ReadFull(r.r, r.b[:4])
-	r.tot += 4
+	atomic.AddUint64(&r.tot, 8)
 	return uint32(r.b[3]) | uint32(r.b[2])<<8 | uint32(r.b[1])<<16 | uint32(r.b[0])<<24
 }
 
@@ -127,7 +132,11 @@ func (r *marshalReader) readUint64() uint64 {
 		return 0
 	}
 	_, r.err = io.ReadFull(r.r, r.b[:8])
-	r.tot += 8
+	atomic.AddUint64(&r.tot, 8)
 	return uint64(r.b[7]) | uint64(r.b[6])<<8 | uint64(r.b[5])<<16 | uint64(r.b[4])<<24 |
 		uint64(r.b[3])<<32 | uint64(r.b[2])<<40 | uint64(r.b[1])<<48 | uint64(r.b[0])<<56
 }
+
+func (r *marshalReader) getTot() uint64 {
+	return atomic.LoadUint64(&r.tot)
+}
diff --git a/protocol/messages.go b/protocol/messages.go
index 3328bddc5..9b273a222 100644
--- a/protocol/messages.go
+++ b/protocol/messages.go
@@ -50,7 +50,7 @@ func (w *marshalWriter) writeIndex(idx []FileInfo) {
 func WriteIndex(w io.Writer, idx []FileInfo) (int, error) {
 	mw := marshalWriter{w: w}
 	mw.writeIndex(idx)
-	return mw.tot, mw.err
+	return int(mw.getTot()), mw.err
 }
 
 func (w *marshalWriter) writeRequest(r request) {
diff --git a/protocol/protocol.go b/protocol/protocol.go
index d659cb849..cc8f6e776 100644
--- a/protocol/protocol.go
+++ b/protocol/protocol.go
@@ -46,18 +46,20 @@ type Model interface {
 type Connection struct {
 	sync.RWMutex
 
-	ID             string
-	receiver       Model
-	reader         io.Reader
-	mreader        *marshalReader
-	writer         io.Writer
-	mwriter        *marshalWriter
-	closed         bool
-	awaiting       map[int]chan asyncResult
-	nextId         int
-	peerLatency    time.Duration
+	ID          string
+	receiver    Model
+	reader      io.Reader
+	mreader     *marshalReader
+	writer      io.Writer
+	mwriter     *marshalWriter
+	closed      bool
+	awaiting    map[int]chan asyncResult
+	nextId      int
+	peerLatency time.Duration
+	indexSent   map[string]int64
+
 	lastStatistics Statistics
-	indexSent      map[string]int64
+	statisticsLock sync.Mutex
 
 	lastReceive     time.Time
 	lastReceiveLock sync.RWMutex
@@ -371,16 +373,18 @@ type Statistics struct {
 }
 
 func (c *Connection) Statistics() Statistics {
-	c.Lock()
-	defer c.Unlock()
+	c.statisticsLock.Lock()
+	defer c.statisticsLock.Unlock()
 
 	secs := time.Since(c.lastStatistics.At).Seconds()
+	rt := int(c.mreader.getTot())
+	wt := int(c.mwriter.getTot())
 	stats := Statistics{
 		At:             time.Now(),
-		InBytesTotal:   c.mreader.tot,
-		InBytesPerSec:  int(float64(c.mreader.tot-c.lastStatistics.InBytesTotal) / secs),
-		OutBytesTotal:  c.mwriter.tot,
-		OutBytesPerSec: int(float64(c.mwriter.tot-c.lastStatistics.OutBytesTotal) / secs),
+		InBytesTotal:   rt,
+		InBytesPerSec:  int(float64(rt-c.lastStatistics.InBytesTotal) / secs),
+		OutBytesTotal:  wt,
+		OutBytesPerSec: int(float64(wt-c.lastStatistics.OutBytesTotal) / secs),
 		Latency:        c.peerLatency,
 	}
 	c.lastStatistics = stats