diff --git a/lib/tasks/tts-task.js b/lib/tasks/tts-task.js
index 65b43641..41598f85 100644
--- a/lib/tasks/tts-task.js
+++ b/lib/tasks/tts-task.js
@@ -144,7 +144,7 @@ class TtsTask extends Task {
         obj = {
           GOOGLE_TTS_LANGUAGE_CODE: language,
           GOOGLE_TTS_VOICE_NAME: voice,
-          GOOGLE_APPLICATION_CREDENTIALS: JSON.stringify(credentials)
+          GOOGLE_APPLICATION_CREDENTIALS: JSON.stringify(credentials.credentials)
         };
         break;
       default: