diff --git a/webrtc/modules/utility/source/file_recorder_impl.cc b/webrtc/modules/utility/source/file_recorder_impl.cc
index 032869c72b..7e13c369e9 100644
--- a/webrtc/modules/utility/source/file_recorder_impl.cc
+++ b/webrtc/modules/utility/source/file_recorder_impl.cc
@@ -715,6 +715,8 @@ int32_t AviRecorder::WriteEncodedAudioData(
     uint16_t millisecondsOfData,
     const TickTime* playoutTS)
 {
+    CriticalSectionScoped lock(_critSec);
+
     if (!IsRecording())
     {
         return -1;