diff --git a/pc/rtp_sender.cc b/pc/rtp_sender.cc
index 6ef7f9f873..9eaed311a7 100644
--- a/pc/rtp_sender.cc
+++ b/pc/rtp_sender.cc
@@ -10,6 +10,7 @@
 
 #include "pc/rtp_sender.h"
 
+#include <atomic>
 #include <utility>
 #include <vector>
 
@@ -28,9 +29,11 @@ namespace webrtc {
 
 namespace {
 
-// This function is only expected to be called on the signalling thread.
+// This function is only expected to be called on the signaling thread.
+// On the other hand, some test or even production setups may use
+// several signaling threads.
 int GenerateUniqueId() {
-  static int g_unique_id = 0;
+  static std::atomic<int> g_unique_id{0};
 
   return ++g_unique_id;
 }