diff --git a/packages/text-to-speech/src/realisticTextToSpeech.ts b/packages/text-to-speech/src/realisticTextToSpeech.ts
index 1cb28decd..329058611 100644
--- a/packages/text-to-speech/src/realisticTextToSpeech.ts
+++ b/packages/text-to-speech/src/realisticTextToSpeech.ts
@@ -76,6 +76,7 @@ export class RealisticTextToSpeech implements TextToSpeech {
 
     return {
       audioData,
+      speechMarks: [],
     }
   }
 
diff --git a/packages/text-to-speech/src/textToSpeech.ts b/packages/text-to-speech/src/textToSpeech.ts
index c489eabd7..3bc6f7b4b 100644
--- a/packages/text-to-speech/src/textToSpeech.ts
+++ b/packages/text-to-speech/src/textToSpeech.ts
@@ -11,7 +11,7 @@ export interface TextToSpeechInput {
 
 export interface TextToSpeechOutput {
   audioData?: Buffer
-  speechMarks?: SpeechMark[]
+  speechMarks: SpeechMark[]
 }
 
 export interface SpeechMark {