diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index 45c68b5..5991eab 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -37,6 +37,7 @@
 #include <cpustats/ThreadCpuUsage.h>
 #endif
 #endif
+#include <audio_utils/conversion.h>
 #include <audio_utils/format.h>
 #include "AudioMixer.h"
 #include "FastMixer.h"
@@ -66,7 +67,8 @@
     mFastTracksGen(0),
     mTotalNativeFramesWritten(0),
     // timestamp
-    mNativeFramesWrittenButNotPresented(0)   // the = 0 is to silence the compiler
+    mNativeFramesWrittenButNotPresented(0),   // the = 0 is to silence the compiler
+    mMasterMono(false)
 {
     // FIXME pass sInitial as parameter to base class constructor, and make it static local
     mPrevious = &sInitial;
@@ -419,6 +421,10 @@
             memset(mMixerBuffer, 0, mMixerBufferSize);
             mMixerBufferState = ZEROED;
         }
+
+        if (mMasterMono.load()) {  // memory_order_seq_cst
+            mono_blend(mMixerBuffer, mMixerBufferFormat, Format_channelCount(mFormat), frameCount);
+        }
         // prepare the buffer used to write to sink
         void *buffer = mSinkBuffer != NULL ? mSinkBuffer : mMixerBuffer;
         if (mFormat.mFormat != mMixerBufferFormat) { // sink format not the same as mixer format