diff --git a/sharing/fake_nearby_connections_manager.cc b/sharing/fake_nearby_connections_manager.cc
index b80800bf..af5199f5 100644
--- a/sharing/fake_nearby_connections_manager.cc
+++ b/sharing/fake_nearby_connections_manager.cc
@@ -57,7 +57,10 @@ void FakeNearbyConnectionsManager::StartAdvertising(
     ConnectionsCallback callback) {
   NL_DCHECK(!IsAdvertising());
   is_shutdown_ = false;
-  advertising_listener_ = listener;
+  {
+    absl::MutexLock lock(&listener_mutex_);
+    advertising_listener_ = listener;
+  }
   advertising_data_usage_ = data_usage;
   advertising_power_level_ = power_level;
   advertising_endpoint_info_ = std::move(endpoint_info);
@@ -73,7 +76,10 @@ void FakeNearbyConnectionsManager::StopAdvertising(
     ConnectionsCallback callback) {
   NL_DCHECK(IsAdvertising());
   NL_DCHECK(!is_shutdown());
-  advertising_listener_ = nullptr;
+  {
+    absl::MutexLock lock(&listener_mutex_);
+    advertising_listener_ = nullptr;
+  }
   advertising_data_usage_ = DataUsage::UNKNOWN_DATA_USAGE;
   advertising_power_level_ = PowerLevel::kUnknown;
   advertising_endpoint_info_.reset();
@@ -89,6 +95,7 @@ void FakeNearbyConnectionsManager::StartDiscovery(
     DiscoveryListener* listener, DataUsage data_usage,
     ConnectionsCallback callback) {
   is_shutdown_ = false;
+  absl::MutexLock lock(&listener_mutex_);
   discovery_listener_ = listener;
   std::move(callback)(Status::kSuccess);
 }
@@ -96,6 +103,7 @@ void FakeNearbyConnectionsManager::StartDiscovery(
 void FakeNearbyConnectionsManager::StopDiscovery() {
   NL_DCHECK(IsDiscovering());
   NL_DCHECK(!is_shutdown());
+  absl::MutexLock lock(&listener_mutex_);
   discovery_listener_ = nullptr;
 }
 
@@ -204,23 +212,33 @@ void FakeNearbyConnectionsManager::UpgradeBandwidth(
 void FakeNearbyConnectionsManager::OnEndpointFound(
     absl::string_view endpoint_id,
     std::unique_ptr<DiscoveredEndpointInfo> info) {
-  if (discovery_listener_ == nullptr) return;
-
-  discovery_listener_->OnEndpointDiscovered(endpoint_id, info->endpoint_info);
+  DiscoveryListener* listener = nullptr;
+  {
+    absl::MutexLock lock(&listener_mutex_);
+    listener = discovery_listener_;
+  }
+  if (listener == nullptr) return;
+  listener->OnEndpointDiscovered(endpoint_id, info->endpoint_info);
 }
 
 void FakeNearbyConnectionsManager::OnEndpointLost(
     absl::string_view endpoint_id) {
-  if (!discovery_listener_) return;
-
-  discovery_listener_->OnEndpointLost(endpoint_id);
+  DiscoveryListener* listener = nullptr;
+  {
+    absl::MutexLock lock(&listener_mutex_);
+    listener = discovery_listener_;
+  }
+  if (listener == nullptr) return;
+  listener->OnEndpointLost(endpoint_id);
 }
 
 bool FakeNearbyConnectionsManager::IsAdvertising() const {
+  absl::MutexLock lock(&listener_mutex_);
   return advertising_listener_ != nullptr;
 }
 
 bool FakeNearbyConnectionsManager::IsDiscovering() const {
+  absl::MutexLock lock(&listener_mutex_);
   return discovery_listener_ != nullptr;
 }
 
@@ -264,6 +282,7 @@ FakeNearbyConnectionsManager::GetRegisteredPayloadPath(int64_t payload_id) {
 }
 
 void FakeNearbyConnectionsManager::CleanupForProcessStopped() {
+  absl::MutexLock lock(&listener_mutex_);
   advertising_listener_ = nullptr;
   advertising_data_usage_ = DataUsage::UNKNOWN_DATA_USAGE;
   advertising_power_level_ = PowerLevel::kUnknown;
diff --git a/sharing/fake_nearby_connections_manager.h b/sharing/fake_nearby_connections_manager.h
index 8a8a557d..085b85e9 100644
--- a/sharing/fake_nearby_connections_manager.h
+++ b/sharing/fake_nearby_connections_manager.h
@@ -146,8 +146,11 @@ class FakeNearbyConnectionsManager : public NearbyConnectionsManager {
   void HandleStartAdvertisingCallback(ConnectionsStatus status);
   void HandleStopAdvertisingCallback(ConnectionsStatus status);
 
-  IncomingConnectionListener* advertising_listener_ = nullptr;
-  DiscoveryListener* discovery_listener_ = nullptr;
+  mutable absl::Mutex listener_mutex_;
+  IncomingConnectionListener* advertising_listener_
+      ABSL_GUARDED_BY(listener_mutex_) = nullptr;
+  DiscoveryListener* discovery_listener_ ABSL_GUARDED_BY(listener_mutex_) =
+      nullptr;
   bool is_shutdown_ = false;
   proto::DataUsage advertising_data_usage_ =
       proto::DataUsage::UNKNOWN_DATA_USAGE;