diff --git a/lib/synth-audio.js b/lib/synth-audio.js
index 119e14a..b2c491c 100644
--- a/lib/synth-audio.js
+++ b/lib/synth-audio.js
@@ -326,7 +326,7 @@ const synthMicrosoft = async(logger, {
               break;
             case ResultReason.SynthesizingAudioCompleted:
               stats.increment('tts.count', ['vendor:microsoft', 'accepted:yes']);
-              resolve(result.audioData);
+              resolve(Buffer.from(result.audioData));
               synthesizer.close();
               break;
             default: