diff --git a/lib/synth-audio.js b/lib/synth-audio.js
index 79ce7cf..9067c89 100644
--- a/lib/synth-audio.js
+++ b/lib/synth-audio.js
@@ -328,7 +328,7 @@ const synthMicrosoft = async(logger, {
             case ResultReason.SynthesizingAudioCompleted:
               stats.increment('tts.count', ['vendor:microsoft', 'accepted:yes']);
               synthesizer.close();
-              resolve(result.audioData());
+              resolve(result.audioData);
               break;
             default:
               logger.info({result}, 'synthAudio: (Microsoft) unexpected result');