diff --git a/lib/middleware.js b/lib/middleware.js
index cf1b07e1..7e1d37e3 100644
--- a/lib/middleware.js
+++ b/lib/middleware.js
@@ -332,7 +332,7 @@ module.exports = function(srf, logger) {
       }
 
       // Resolve application.speech_synthesis_voice if it's custom voice
-      if (app2.speech_synthesis_vendor === 'google' && app2.speech_synthesis_voice.startsWith('custom_')) {
+      if (app2.speech_synthesis_vendor === 'google' && app2.speech_synthesis_voice?.startsWith('custom_')) {
         const arr = /custom_(.*)/.exec(app2.speech_synthesis_voice);
         if (arr) {
           const google_custom_voice_sid = arr[1];