diff --git a/api/peerconnectioninterface.cc b/api/peerconnectioninterface.cc
index a861801389..665760c973 100644
--- a/api/peerconnectioninterface.cc
+++ b/api/peerconnectioninterface.cc
@@ -178,6 +178,7 @@ bool PeerConnectionInterface::StartRtcEventLog(
 
 rtc::scoped_refptr<DtlsTransportInterface>
 PeerConnectionInterface::LookupDtlsTransportByMid(const std::string& mid) {
+  RTC_NOTREACHED();
   return nullptr;
 }
 
diff --git a/api/peerconnectioninterface.h b/api/peerconnectioninterface.h
index 02b925dc99..4a7b051b33 100644
--- a/api/peerconnectioninterface.h
+++ b/api/peerconnectioninterface.h
@@ -1034,9 +1034,9 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
   // In the Javascript API, DtlsTransport is a property of a sender, but
   // because the PeerConnection owns the DtlsTransport in this implementation,
   // it is better to look them up on the PeerConnection.
+  // TODO(hta): Remove default implementation after updating Chrome.
   virtual rtc::scoped_refptr<DtlsTransportInterface> LookupDtlsTransportByMid(
       const std::string& mid);
-  // TODO(hta): Remove default implementation.
 
   // Returns the current SignalingState.
   virtual SignalingState signaling_state() = 0;
diff --git a/api/peerconnectionproxy.h b/api/peerconnectionproxy.h
index 6b66bccc4e..9637c0aae7 100644
--- a/api/peerconnectionproxy.h
+++ b/api/peerconnectionproxy.h
@@ -119,6 +119,9 @@ PROXY_METHOD1(bool,
               const std::vector<cricket::Candidate>&);
 PROXY_METHOD1(void, SetAudioPlayout, bool)
 PROXY_METHOD1(void, SetAudioRecording, bool)
+PROXY_METHOD1(rtc::scoped_refptr<DtlsTransportInterface>,
+              LookupDtlsTransportByMid,
+              const std::string&)
 PROXY_METHOD1(RTCError, SetBitrate, const BitrateSettings&);
 PROXY_METHOD1(void,
               SetBitrateAllocationStrategy,
diff --git a/pc/test/fakepeerconnectionbase.h b/pc/test/fakepeerconnectionbase.h
index c190628beb..b4bc7b93f0 100644
--- a/pc/test/fakepeerconnectionbase.h
+++ b/pc/test/fakepeerconnectionbase.h
@@ -189,6 +189,11 @@ class FakePeerConnectionBase : public PeerConnectionInternal {
 
   void SetAudioRecording(bool recording) override {}
 
+  rtc::scoped_refptr<DtlsTransportInterface> LookupDtlsTransportByMid(
+      const std::string& mid) {
+    return nullptr;
+  }
+
   SignalingState signaling_state() override { return SignalingState::kStable; }
 
   IceConnectionState ice_connection_state() override {