diff --git a/api/rtp_parameters.cc b/api/rtp_parameters.cc
index b51ea7db3c..2b1abe0eff 100644
--- a/api/rtp_parameters.cc
+++ b/api/rtp_parameters.cc
@@ -167,6 +167,7 @@ constexpr int RtpExtension::kOneByteHeaderExtensionMaxValueSize;
 bool RtpExtension::IsSupportedForAudio(const std::string& uri) {
   return uri == webrtc::RtpExtension::kAudioLevelUri ||
          uri == webrtc::RtpExtension::kTransportSequenceNumberUri ||
+         uri == webrtc::RtpExtension::kTransportSequenceNumberV2Uri ||
          uri == webrtc::RtpExtension::kMidUri ||
          uri == webrtc::RtpExtension::kRidUri ||
          uri == webrtc::RtpExtension::kRepairedRidUri;
@@ -177,6 +178,7 @@ bool RtpExtension::IsSupportedForVideo(const std::string& uri) {
          uri == webrtc::RtpExtension::kAbsSendTimeUri ||
          uri == webrtc::RtpExtension::kVideoRotationUri ||
          uri == webrtc::RtpExtension::kTransportSequenceNumberUri ||
+         uri == webrtc::RtpExtension::kTransportSequenceNumberV2Uri ||
          uri == webrtc::RtpExtension::kPlayoutDelayUri ||
          uri == webrtc::RtpExtension::kVideoContentTypeUri ||
          uri == webrtc::RtpExtension::kVideoTimingUri ||
@@ -202,6 +204,7 @@ bool RtpExtension::IsEncryptionSupported(const std::string& uri) {
 #endif
          uri == webrtc::RtpExtension::kVideoRotationUri ||
          uri == webrtc::RtpExtension::kTransportSequenceNumberUri ||
+         uri == webrtc::RtpExtension::kTransportSequenceNumberV2Uri ||
          uri == webrtc::RtpExtension::kPlayoutDelayUri ||
          uri == webrtc::RtpExtension::kVideoContentTypeUri ||
          uri == webrtc::RtpExtension::kMidUri ||
diff --git a/pc/media_session.cc b/pc/media_session.cc
index 19eb769dfc..5e6b97bb43 100644
--- a/pc/media_session.cc
+++ b/pc/media_session.cc
@@ -1091,16 +1091,41 @@ static void NegotiateRtpHeaderExtensions(
     const RtpHeaderExtensions& local_extensions,
     const RtpHeaderExtensions& offered_extensions,
     bool enable_encrypted_rtp_header_extensions,
-    RtpHeaderExtensions* negotiated_extenstions) {
+    RtpHeaderExtensions* negotiated_extensions) {
+  // TransportSequenceNumberV2 is not offered by default. The special logic for
+  // the TransportSequenceNumber extensions works as follows:
+  // Offer       Answer
+  // V1          V1 if in local_extensions.
+  // V1 and V2   V2 regardless of local_extensions.
+  // V2          V2 regardless of local_extensions.
+  const webrtc::RtpExtension* transport_sequence_number_v2_offer =
+      webrtc::RtpExtension::FindHeaderExtensionByUri(
+          offered_extensions,
+          webrtc::RtpExtension::kTransportSequenceNumberV2Uri);
+
   for (const webrtc::RtpExtension& ours : local_extensions) {
     webrtc::RtpExtension theirs;
     if (FindByUriWithEncryptionPreference(
             offered_extensions, ours, enable_encrypted_rtp_header_extensions,
             &theirs)) {
-      // We respond with their RTP header extension id.
-      negotiated_extenstions->push_back(theirs);
+      if (transport_sequence_number_v2_offer &&
+          ours.uri == webrtc::RtpExtension::kTransportSequenceNumberUri) {
+        // Don't respond to
+        // http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01
+        // if we get an offer including
+        // http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-02
+        continue;
+      } else {
+        // We respond with their RTP header extension id.
+        negotiated_extensions->push_back(theirs);
+      }
     }
   }
+
+  if (transport_sequence_number_v2_offer) {
+    // Respond that we support kTransportSequenceNumberV2Uri.
+    negotiated_extensions->push_back(*transport_sequence_number_v2_offer);
+  }
 }
 
 static void StripCNCodecs(AudioCodecs* audio_codecs) {
diff --git a/pc/media_session_unittest.cc b/pc/media_session_unittest.cc
index 3f7631eccf..e876c36301 100644
--- a/pc/media_session_unittest.cc
+++ b/pc/media_session_unittest.cc
@@ -213,6 +213,27 @@ static const RtpExtension kVideoRtpExtensionEncryptedAnswer[] = {
     RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 11, true),
 };
 
+static const RtpExtension kRtpExtensionTransportSequenceNumber01[] = {
+    RtpExtension("http://www.ietf.org/id/"
+                 "draft-holmer-rmcat-transport-wide-cc-extensions-01",
+                 1),
+};
+
+static const RtpExtension kRtpExtensionTransportSequenceNumber01And02[] = {
+    RtpExtension("http://www.ietf.org/id/"
+                 "draft-holmer-rmcat-transport-wide-cc-extensions-01",
+                 1),
+    RtpExtension("http://www.ietf.org/id/"
+                 "draft-holmer-rmcat-transport-wide-cc-extensions-02",
+                 2),
+};
+
+static const RtpExtension kRtpExtensionTransportSequenceNumber02[] = {
+    RtpExtension("http://www.ietf.org/id/"
+                 "draft-holmer-rmcat-transport-wide-cc-extensions-02",
+                 2),
+};
+
 static const uint32_t kSimulcastParamsSsrc[] = {10, 11, 20, 21, 30, 31};
 static const uint32_t kSimSsrc[] = {10, 20, 30};
 static const uint32_t kFec1Ssrc[] = {10, 11};
@@ -689,6 +710,30 @@ class MediaSessionDescriptionFactoryTest : public testing::Test {
     EXPECT_EQ(cricket::kMediaProtocolSavpf, vcd->protocol());
   }
 
+  void TestTransportSequenceNumberNegotiation(
+      const cricket::RtpHeaderExtensions& local,
+      const cricket::RtpHeaderExtensions& offered,
+      const cricket::RtpHeaderExtensions& expectedAnswer) {
+    MediaSessionOptions opts;
+    AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+    f1_.set_audio_rtp_header_extensions(offered);
+    f1_.set_video_rtp_header_extensions(offered);
+    f2_.set_audio_rtp_header_extensions(local);
+    f2_.set_video_rtp_header_extensions(local);
+
+    std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+    ASSERT_TRUE(offer.get() != NULL);
+    std::unique_ptr<SessionDescription> answer =
+        f2_.CreateAnswer(offer.get(), opts, NULL);
+
+    EXPECT_EQ(
+        expectedAnswer,
+        GetFirstAudioContentDescription(answer.get())->rtp_header_extensions());
+    EXPECT_EQ(
+        expectedAnswer,
+        GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
+  }
+
  protected:
   UniqueRandomIdGenerator ssrc_generator1;
   UniqueRandomIdGenerator ssrc_generator2;
@@ -1506,6 +1551,32 @@ TEST_F(MediaSessionDescriptionFactoryTest, TestOfferAnswerWithRtpExtensions) {
       GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
 }
 
+// Create a audio/video offer and answer and ensure that the
+// TransportSequenceNumber RTP header extensions are handled correctly. 02 is
+// supported and should take precedence even though not listed among locally
+// supported extensions.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithTransportSequenceNumberInOffer) {
+  TestTransportSequenceNumberNegotiation(
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),   // Local.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),   // Offer.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01));  // Expected answer.
+}
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithTransportSequenceNumber01And02InOffer) {
+  TestTransportSequenceNumberNegotiation(
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),       // Local.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01And02),  // Offer.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber02));  // Expected answer.
+}
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithTransportSequenceNumber02InOffer) {
+  TestTransportSequenceNumberNegotiation(
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),   // Local.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber02),   // Offer.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber02));  // Expected answer.
+}
+
 TEST_F(MediaSessionDescriptionFactoryTest,
        TestOfferAnswerWithEncryptedRtpExtensionsBoth) {
   MediaSessionOptions opts;