diff --git a/lib/middleware.js b/lib/middleware.js
index 41a2a75d..e71c054a 100644
--- a/lib/middleware.js
+++ b/lib/middleware.js
@@ -299,22 +299,30 @@ module.exports = function(srf, logger) {
       if (app.app_json) {
         json = JSON.parse(app.app_json);
       } else {
+        const defaults = {
+          synthesizer: {
+            vendor: app.speech_synthesis_vendor,
+            ...(app.speech_synthesis_label && {label: app.speech_synthesis_label}),
+            language: app.speech_synthesis_language,
+            voice: app.speech_synthesis_voice,
+            ...(app.fallback_speech_synthesis_vendor && {fallback_vendor: app.fallback_speech_synthesis_vendor}),
+            ...(app.fallback_speech_synthesis_label && {fallback_label: app.fallback_speech_synthesis_label}),
+            ...(app.fallback_speech_synthesis_language && {fallback_language: app.fallback_speech_synthesis_language}),
+            ...(app.fallback_speech_synthesis_voice && {fallback_voice: app.fallback_speech_synthesis_voice})
+          },
+          recognizer: {
+            vendor: app.speech_recognizer_vendor,
+            ...(app.speech_synthesis_label && {label: app.speech_synthesis_label}),
+            language: app.speech_recognizer_language,
+            ...(app.fallback_speech_recognizer_vendor && {fallback_vendor: app.fallback_speech_recognizer_vendor}),
+            ...(app.fallback_speech_recognizer_label && {fallback_label: app.fallback_speech_recognizer_label}),
+            ...(app.fallback_speech_recognizer_language && {fallback_language: app.fallback_speech_recognizer_language})
+          }
+        };
         const params = Object.assign(['POST', 'WS'].includes(app.call_hook.method) ? { sip: req.msg } : {},
           req.locals.callInfo,
           { service_provider_sid: req.locals.service_provider_sid },
-          {
-            defaults: {
-              synthesizer: {
-                vendor: app.speech_synthesis_vendor,
-                language: app.speech_synthesis_language,
-                voice: app.speech_synthesis_voice
-              },
-              recognizer: {
-                vendor: app.speech_recognizer_vendor,
-                language: app.speech_recognizer_language
-              }
-            }
-          });
+          { defaults });
         logger.debug({ params }, 'sending initial webhook');
         const obj = rootSpan.startChildSpan('performAppWebhook');
         span = obj.span;