diff --git a/webrtc/voice_engine/level_indicator.cc b/webrtc/voice_engine/level_indicator.cc
index 1b5cba579e..a32527c2d8 100644
--- a/webrtc/voice_engine/level_indicator.cc
+++ b/webrtc/voice_engine/level_indicator.cc
@@ -8,6 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include "critical_section_wrapper.h"
 #include "level_indicator.h"
 #include "module_common_types.h"
 #include "signal_processing_library.h"
@@ -16,7 +17,6 @@ namespace webrtc {
 
 namespace voe {
 
-
 // Number of bars on the indicator.
 // Note that the number of elements is specified because we are indexing it
 // in the range of 0-32
@@ -25,28 +25,26 @@ const WebRtc_Word8 permutation[33] =
 
 
 AudioLevel::AudioLevel() :
+    _critSect(*CriticalSectionWrapper::CreateCriticalSection()),
     _absMax(0),
     _count(0),
     _currentLevel(0),
-    _currentLevelFullRange(0)
-{
+    _currentLevelFullRange(0) {
 }
 
-AudioLevel::~AudioLevel()
-{
+AudioLevel::~AudioLevel() {
 }
 
-void
-AudioLevel::Clear()
+void AudioLevel::Clear()
 {
+    CriticalSectionScoped cs(&_critSect);
     _absMax = 0;
     _count = 0;
     _currentLevel = 0;
     _currentLevelFullRange = 0;
 }
 
-void
-AudioLevel::ComputeLevel(const AudioFrame& audioFrame)
+void AudioLevel::ComputeLevel(const AudioFrame& audioFrame)
 {
     WebRtc_Word16 absValue(0);
 
@@ -54,6 +52,11 @@ AudioLevel::ComputeLevel(const AudioFrame& audioFrame)
     absValue = WebRtcSpl_MaxAbsValueW16(
         audioFrame.data_,
         audioFrame.samples_per_channel_*audioFrame.num_channels_);
+
+    // Protect member access using a lock since this method is called on a
+    // dedicated audio thread in the RecordedDataIsAvailable() callback.
+    CriticalSectionScoped cs(&_critSect);
+
     if (absValue > _absMax)
     _absMax = absValue;
 
@@ -82,15 +85,15 @@ AudioLevel::ComputeLevel(const AudioFrame& audioFrame)
     }
 }
 
-WebRtc_Word8
-AudioLevel::Level() const
+WebRtc_Word8 AudioLevel::Level() const
 {
+    CriticalSectionScoped cs(&_critSect);
     return _currentLevel;
 }
 
-WebRtc_Word16
-AudioLevel::LevelFullRange() const
+WebRtc_Word16 AudioLevel::LevelFullRange() const
 {
+    CriticalSectionScoped cs(&_critSect);
     return _currentLevelFullRange;
 }
 
diff --git a/webrtc/voice_engine/level_indicator.h b/webrtc/voice_engine/level_indicator.h
index 564b068ef7..2041b1bbb8 100644
--- a/webrtc/voice_engine/level_indicator.h
+++ b/webrtc/voice_engine/level_indicator.h
@@ -17,6 +17,7 @@
 namespace webrtc {
 
 class AudioFrame;
+class CriticalSectionWrapper;
 namespace voe {
 
 class AudioLevel
@@ -25,17 +26,22 @@ public:
     AudioLevel();
     virtual ~AudioLevel();
 
-    void ComputeLevel(const AudioFrame& audioFrame);
-
+    // Called on "API thread(s)" from APIs like VoEBase::CreateChannel(),
+    // VoEBase::StopSend(), VoEVolumeControl::GetSpeechOutputLevel().
     WebRtc_Word8 Level() const;
-
     WebRtc_Word16 LevelFullRange() const;
-
     void Clear();
 
+    // Called on a native capture audio thread (platform dependent) from the
+    // AudioTransport::RecordedDataIsAvailable() callback.
+    // In Chrome, this method is called on the AudioInputDevice thread.
+    void ComputeLevel(const AudioFrame& audioFrame);
+
 private:
     enum { kUpdateFrequency = 10};
 
+    CriticalSectionWrapper& _critSect;
+
     WebRtc_Word16 _absMax;
     WebRtc_Word16 _count;
     WebRtc_Word8 _currentLevel;