diff --git a/modules/pacing/packet_router.cc b/modules/pacing/packet_router.cc
index de2621790b..a14c65e719 100644
--- a/modules/pacing/packet_router.cc
+++ b/modules/pacing/packet_router.cc
@@ -149,9 +149,8 @@ void PacketRouter::SendPacket(std::unique_ptr<RtpPacketToSend> packet,
   rtc::CritScope cs(&modules_crit_);
   // With the new pacer code path, transport sequence numbers are only set here,
   // on the pacer thread. Therefore we don't need atomics/synchronization.
-  if (packet->IsExtensionReserved<TransportSequenceNumber>() &&
-      packet->SetExtension<TransportSequenceNumber>(transport_seq_)) {
-    ++transport_seq_;
+  if (packet->IsExtensionReserved<TransportSequenceNumber>()) {
+    packet->SetExtension<TransportSequenceNumber>(++transport_seq_);
   }
 
   auto it = rtp_module_cache_map_.find(packet->Ssrc());
diff --git a/modules/pacing/packet_router_unittest.cc b/modules/pacing/packet_router_unittest.cc
index ac59a4424d..ff1c6f988a 100644
--- a/modules/pacing/packet_router_unittest.cc
+++ b/modules/pacing/packet_router_unittest.cc
@@ -978,7 +978,8 @@ TEST(PacketRouterTest, SendPacketAssignsTransportSequenceNumbers) {
   extension_manager.Register(kRtpExtensionTransportSequenceNumber,
                              kTransportSequenceNumberExtensionId);
 
-  uint16_t transport_sequence_number = 0;
+  // Transport sequence numbers start at 1, for historical reasons.
+  uint16_t transport_sequence_number = 1;
 
   auto packet = absl::make_unique<RtpPacketToSend>(&extension_manager);
   EXPECT_TRUE(packet->ReserveExtension<TransportSequenceNumber>());