diff --git a/internal/ackhandler/sent_packet_handler.go b/internal/ackhandler/sent_packet_handler.go
index 7e7a1a10c..e807226e8 100644
--- a/internal/ackhandler/sent_packet_handler.go
+++ b/internal/ackhandler/sent_packet_handler.go
@@ -292,10 +292,13 @@ func (h *sentPacketHandler) ReceivedAck(ack *wire.AckFrame, encLevel protocol.En
 		}
 	}
 
-	if h.qlogger != nil && h.ptoCount != 0 {
-		h.qlogger.UpdatedPTOCount(0)
+	// Reset the pto_count unless the client is unsure if the server has validated the client's address.
+	if h.peerCompletedAddressValidation {
+		if h.qlogger != nil && h.ptoCount != 0 {
+			h.qlogger.UpdatedPTOCount(0)
+		}
+		h.ptoCount = 0
 	}
-	h.ptoCount = 0
 	h.numProbesToSend = 0
 
 	h.setLossDetectionTimer()
diff --git a/internal/ackhandler/sent_packet_handler_test.go b/internal/ackhandler/sent_packet_handler_test.go
index bdff4896a..c0e279090 100644
--- a/internal/ackhandler/sent_packet_handler_test.go
+++ b/internal/ackhandler/sent_packet_handler_test.go
@@ -601,6 +601,19 @@ var _ = Describe("SentPacketHandler", func() {
 			Expect(handler.GetLossDetectionTimeout().Sub(sendTime)).To(Equal(4 * timeout))
 		})
 
+		It("reset the PTO count when receiving an ACK", func() {
+			now := time.Now()
+			handler.SetHandshakeComplete()
+			handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 1, SendTime: now.Add(-time.Minute)}))
+			handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 2, SendTime: now.Add(-time.Minute)}))
+			Expect(handler.GetLossDetectionTimeout()).To(BeTemporally("~", now.Add(-time.Minute), time.Second))
+			Expect(handler.OnLossDetectionTimeout()).To(Succeed())
+			Expect(handler.SendMode()).To(Equal(SendPTOAppData))
+			Expect(handler.ptoCount).To(BeEquivalentTo(1))
+			Expect(handler.ReceivedAck(&wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 1, Largest: 1}}}, protocol.Encryption1RTT, time.Now())).To(Succeed())
+			Expect(handler.ptoCount).To(BeZero())
+		})
+
 		It("resets the PTO mode and PTO count when a packet number space is dropped", func() {
 			now := time.Now()
 			handler.SentPacket(ackElicitingPacket(&Packet{
@@ -808,6 +821,18 @@ var _ = Describe("SentPacketHandler", func() {
 			Expect(pto).ToNot(BeZero())
 			Expect(handler.GetLossDetectionTimeout()).To(BeTemporally("~", time.Now().Add(pto), 10*time.Millisecond))
 		})
+
+		It("doesn't reset the PTO count when receiving an ACK", func() {
+			now := time.Now()
+			handler.SentPacket(initialPacket(&Packet{PacketNumber: 1, SendTime: now.Add(-time.Minute)}))
+			handler.SentPacket(initialPacket(&Packet{PacketNumber: 2, SendTime: now.Add(-time.Minute)}))
+			Expect(handler.GetLossDetectionTimeout()).To(BeTemporally("~", now.Add(-time.Minute), time.Second))
+			Expect(handler.OnLossDetectionTimeout()).To(Succeed())
+			Expect(handler.SendMode()).To(Equal(SendPTOInitial))
+			Expect(handler.ptoCount).To(BeEquivalentTo(1))
+			Expect(handler.ReceivedAck(&wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 1, Largest: 1}}}, protocol.EncryptionInitial, time.Now())).To(Succeed())
+			Expect(handler.ptoCount).To(BeEquivalentTo(1))
+		})
 	})
 
 	Context("Packet-based loss detection", func() {