diff --git a/test/pc/e2e/BUILD.gn b/test/pc/e2e/BUILD.gn
index 08df2f8817..1befff95bf 100644
--- a/test/pc/e2e/BUILD.gn
+++ b/test/pc/e2e/BUILD.gn
@@ -498,6 +498,8 @@ if (!build_with_chromium) {
         "../../../api:rtc_stats_api",
         "../../../api:stats_observer_interface",
         "../../../rtc_base:logging",
+        "../../../rtc_base:rtc_base_approved",
+        "../../../rtc_base/synchronization:mutex",
       ]
     }
 
diff --git a/test/pc/e2e/stats_poller.cc b/test/pc/e2e/stats_poller.cc
index 5f1424cd29..ecf640be29 100644
--- a/test/pc/e2e/stats_poller.cc
+++ b/test/pc/e2e/stats_poller.cc
@@ -13,6 +13,7 @@
 #include <utility>
 
 #include "rtc_base/logging.h"
+#include "rtc_base/synchronization/mutex.h"
 
 namespace webrtc {
 namespace webrtc_pc_e2e {
@@ -29,18 +30,28 @@ void InternalStatsObserver::OnStatsDelivered(
 }
 
 StatsPoller::StatsPoller(std::vector<StatsObserverInterface*> observers,
-                         std::map<std::string, TestPeer*> peers) {
+                         std::map<std::string, TestPeer*> peers)
+    : observers_(observers) {
+  webrtc::MutexLock lock(&mutex_);
   for (auto& peer : peers) {
     pollers_.push_back(rtc::make_ref_counted<InternalStatsObserver>(
-        peer.first, peer.second, observers));
+        peer.first, peer.second, observers_));
   }
 }
 
 void StatsPoller::PollStatsAndNotifyObservers() {
+  webrtc::MutexLock lock(&mutex_);
   for (auto& poller : pollers_) {
     poller->PollStats();
   }
 }
 
+void StatsPoller::RegisterParticipantInCall(absl::string_view peer_name,
+                                            TestPeer* peer) {
+  webrtc::MutexLock lock(&mutex_);
+  pollers_.push_back(rtc::make_ref_counted<InternalStatsObserver>(
+      peer_name, peer, observers_));
+}
+
 }  // namespace webrtc_pc_e2e
 }  // namespace webrtc
diff --git a/test/pc/e2e/stats_poller.h b/test/pc/e2e/stats_poller.h
index 157a147834..2b3f52ca22 100644
--- a/test/pc/e2e/stats_poller.h
+++ b/test/pc/e2e/stats_poller.h
@@ -19,6 +19,8 @@
 #include "api/peer_connection_interface.h"
 #include "api/stats/rtc_stats_collector_callback.h"
 #include "api/test/stats_observer_interface.h"
+#include "rtc_base/synchronization/mutex.h"
+#include "rtc_base/thread_annotations.h"
 #include "test/pc/e2e/test_peer.h"
 
 namespace webrtc {
@@ -28,12 +30,10 @@ namespace webrtc_pc_e2e {
 // objects subscribed.
 class InternalStatsObserver : public RTCStatsCollectorCallback {
  public:
-  InternalStatsObserver(std::string pc_label,
+  InternalStatsObserver(absl::string_view pc_label,
                         TestPeer* peer,
                         std::vector<StatsObserverInterface*> observers)
-      : pc_label_(std::move(pc_label)),
-        peer_(peer),
-        observers_(std::move(observers)) {}
+      : pc_label_(pc_label), peer_(peer), observers_(std::move(observers)) {}
 
   void PollStats();
 
@@ -56,8 +56,13 @@ class StatsPoller {
 
   void PollStatsAndNotifyObservers();
 
+  void RegisterParticipantInCall(absl::string_view peer_name, TestPeer* peer);
+
  private:
-  std::vector<rtc::scoped_refptr<InternalStatsObserver>> pollers_;
+  const std::vector<StatsObserverInterface*> observers_;
+  webrtc::Mutex mutex_;
+  std::vector<rtc::scoped_refptr<InternalStatsObserver>> pollers_
+      RTC_GUARDED_BY(mutex_);
 };
 
 }  // namespace webrtc_pc_e2e