diff --git a/webrtc/modules/audio_processing/audio_processing_impl.cc b/webrtc/modules/audio_processing/audio_processing_impl.cc
index eeb9a79615..1074b61828 100644
--- a/webrtc/modules/audio_processing/audio_processing_impl.cc
+++ b/webrtc/modules/audio_processing/audio_processing_impl.cc
@@ -452,14 +452,15 @@ int AudioProcessingImpl::num_output_channels() const {
 }
 
 void AudioProcessingImpl::set_output_will_be_muted(bool muted) {
-  output_will_be_muted_ = muted;
   CriticalSectionScoped lock(crit_);
+  output_will_be_muted_ = muted;
   if (agc_manager_.get()) {
     agc_manager_->SetCaptureMuted(output_will_be_muted_);
   }
 }
 
 bool AudioProcessingImpl::output_will_be_muted() const {
+  CriticalSectionScoped lock(crit_);
   return output_will_be_muted_;
 }
 
diff --git a/webrtc/modules/audio_processing/audio_processing_impl.h b/webrtc/modules/audio_processing/audio_processing_impl.h
index 765cde7fe1..500f08e82f 100644
--- a/webrtc/modules/audio_processing/audio_processing_impl.h
+++ b/webrtc/modules/audio_processing/audio_processing_impl.h
@@ -210,7 +210,7 @@ class AudioProcessingImpl : public AudioProcessing {
   int delay_offset_ms_;
   bool was_stream_delay_set_;
 
-  bool output_will_be_muted_;
+  bool output_will_be_muted_ GUARDED_BY(crit_);
 
   bool key_pressed_;