diff --git a/webrtc/api/peerconnectioninterface.h b/webrtc/api/peerconnectioninterface.h
index e14b79ca6c..54fae2b711 100644
--- a/webrtc/api/peerconnectioninterface.h
+++ b/webrtc/api/peerconnectioninterface.h
@@ -603,7 +603,7 @@ class PeerConnectionObserver {
   // implement it.
   virtual void OnAddTrack(
       rtc::scoped_refptr<RtpReceiverInterface> receiver,
-      std::vector<rtc::scoped_refptr<MediaStreamInterface>> streams) {}
+      const std::vector<rtc::scoped_refptr<MediaStreamInterface>>& streams) {}
 
  protected:
   // Dtor protected as objects shouldn't be deleted via this interface.
diff --git a/webrtc/api/peerconnectioninterface_unittest.cc b/webrtc/api/peerconnectioninterface_unittest.cc
index 0726c75d4d..d673b4174a 100644
--- a/webrtc/api/peerconnectioninterface_unittest.cc
+++ b/webrtc/api/peerconnectioninterface_unittest.cc
@@ -562,9 +562,10 @@ class MockPeerConnectionObserver : public PeerConnectionObserver {
     callback_triggered_ = true;
   }
 
-  void OnAddTrack(rtc::scoped_refptr<webrtc::RtpReceiverInterface> receiver,
-                  std::vector<rtc::scoped_refptr<webrtc::MediaStreamInterface>>
-                      streams) override {
+  void OnAddTrack(
+      rtc::scoped_refptr<webrtc::RtpReceiverInterface> receiver,
+      const std::vector<rtc::scoped_refptr<webrtc::MediaStreamInterface>>&
+          streams) override {
     EXPECT_TRUE(receiver != nullptr);
     num_added_tracks_++;
     last_added_track_label_ = receiver->id();