diff --git a/mtu_discoverer.go b/mtu_discoverer.go
index 317b09292f6..fdf20157bef 100644
--- a/mtu_discoverer.go
+++ b/mtu_discoverer.go
@@ -2,6 +2,7 @@ package quic
 
 import (
 	"net"
+	"sync/atomic"
 	"time"
 
 	"github.com/quic-go/quic-go/internal/ackhandler"
@@ -47,23 +48,25 @@ type mtuFinder struct {
 
 	rttStats *utils.RTTStats
 	inFlight protocol.ByteCount // the size of the probe packet currently in flight. InvalidByteCount if none is in flight
-	current  protocol.ByteCount
+	current  *atomic.Int64
 	max      protocol.ByteCount // the maximum value, as advertised by the peer (or our maximum size buffer)
 }
 
 var _ mtuDiscoverer = &mtuFinder{}
 
 func newMTUDiscoverer(rttStats *utils.RTTStats, start protocol.ByteCount, mtuIncreased func(protocol.ByteCount)) *mtuFinder {
+	var current atomic.Int64
+	current.Store(int64(start))
 	return &mtuFinder{
 		inFlight:     protocol.InvalidByteCount,
-		current:      start,
+		current:      &current,
 		rttStats:     rttStats,
 		mtuIncreased: mtuIncreased,
 	}
 }
 
 func (f *mtuFinder) done() bool {
-	return f.max-f.current <= maxMTUDiff+1
+	return f.max-f.CurrentSize() <= maxMTUDiff+1
 }
 
 func (f *mtuFinder) Start(maxPacketSize protocol.ByteCount) {
@@ -82,7 +85,7 @@ func (f *mtuFinder) ShouldSendProbe(now time.Time) bool {
 }
 
 func (f *mtuFinder) GetPing() (ackhandler.Frame, protocol.ByteCount) {
-	size := (f.max + f.current) / 2
+	size := (f.max + f.CurrentSize()) / 2
 	f.lastProbeTime = time.Now()
 	f.inFlight = size
 	return ackhandler.Frame{
@@ -92,7 +95,7 @@ func (f *mtuFinder) GetPing() (ackhandler.Frame, protocol.ByteCount) {
 }
 
 func (f *mtuFinder) CurrentSize() protocol.ByteCount {
-	return f.current
+	return protocol.ByteCount(f.current.Load())
 }
 
 type mtuFinderAckHandler mtuFinder
@@ -105,7 +108,7 @@ func (h *mtuFinderAckHandler) OnAcked(wire.Frame) {
 		panic("OnAcked callback called although there's no MTU probe packet in flight")
 	}
 	h.inFlight = protocol.InvalidByteCount
-	h.current = size
+	h.current.Store(int64(size))
 	h.mtuIncreased(size)
 }