diff --git a/lib/synth-audio.js b/lib/synth-audio.js
index 8597b51..e1b8b92 100644
--- a/lib/synth-audio.js
+++ b/lib/synth-audio.js
@@ -435,7 +435,7 @@ const synthGoogle = async(logger, {
     }
 
     let params = '{';
-    params += `credentials=${Buffer.from(JSON.stringify(credentials)).toString('base64')}`;
+    params += `credentials=${Buffer.from(JSON.stringify(credentials.credentials)).toString('base64')}`;
     params += `,playback_id=${key}`;
     params += ',vendor=google';
     params += `,voice=${voice}`;