diff --git a/src/v1/text_to_speech_client.ts b/src/v1/text_to_speech_client.ts
index b7d655e6..81afe573 100644
--- a/src/v1/text_to_speech_client.ts
+++ b/src/v1/text_to_speech_client.ts
@@ -267,7 +267,7 @@ export class TextToSpeechClient {
   // -- Service calls --
   // -------------------
   listVoices(
-    request: protos.google.cloud.texttospeech.v1.IListVoicesRequest,
+    request?: protos.google.cloud.texttospeech.v1.IListVoicesRequest,
     options?: CallOptions
   ): Promise<
     [
@@ -318,7 +318,7 @@ export class TextToSpeechClient {
    * const [response] = await client.listVoices(request);
    */
   listVoices(
-    request: protos.google.cloud.texttospeech.v1.IListVoicesRequest,
+    request?: protos.google.cloud.texttospeech.v1.IListVoicesRequest,
     optionsOrCallback?:
       | CallOptions
       | Callback<
@@ -353,7 +353,7 @@ export class TextToSpeechClient {
     return this.innerApiCalls.listVoices(request, options, callback);
   }
   synthesizeSpeech(
-    request: protos.google.cloud.texttospeech.v1.ISynthesizeSpeechRequest,
+    request?: protos.google.cloud.texttospeech.v1.ISynthesizeSpeechRequest,
     options?: CallOptions
   ): Promise<
     [
@@ -406,7 +406,7 @@ export class TextToSpeechClient {
    * const [response] = await client.synthesizeSpeech(request);
    */
   synthesizeSpeech(
-    request: protos.google.cloud.texttospeech.v1.ISynthesizeSpeechRequest,
+    request?: protos.google.cloud.texttospeech.v1.ISynthesizeSpeechRequest,
     optionsOrCallback?:
       | CallOptions
       | Callback<
diff --git a/src/v1beta1/text_to_speech_client.ts b/src/v1beta1/text_to_speech_client.ts
index 56094247..ef11f945 100644
--- a/src/v1beta1/text_to_speech_client.ts
+++ b/src/v1beta1/text_to_speech_client.ts
@@ -267,7 +267,7 @@ export class TextToSpeechClient {
   // -- Service calls --
   // -------------------
   listVoices(
-    request: protos.google.cloud.texttospeech.v1beta1.IListVoicesRequest,
+    request?: protos.google.cloud.texttospeech.v1beta1.IListVoicesRequest,
     options?: CallOptions
   ): Promise<
     [
@@ -323,7 +323,7 @@ export class TextToSpeechClient {
    * const [response] = await client.listVoices(request);
    */
   listVoices(
-    request: protos.google.cloud.texttospeech.v1beta1.IListVoicesRequest,
+    request?: protos.google.cloud.texttospeech.v1beta1.IListVoicesRequest,
     optionsOrCallback?:
       | CallOptions
       | Callback<
@@ -360,7 +360,7 @@ export class TextToSpeechClient {
     return this.innerApiCalls.listVoices(request, options, callback);
   }
   synthesizeSpeech(
-    request: protos.google.cloud.texttospeech.v1beta1.ISynthesizeSpeechRequest,
+    request?: protos.google.cloud.texttospeech.v1beta1.ISynthesizeSpeechRequest,
     options?: CallOptions
   ): Promise<
     [
@@ -418,7 +418,7 @@ export class TextToSpeechClient {
    * const [response] = await client.synthesizeSpeech(request);
    */
   synthesizeSpeech(
-    request: protos.google.cloud.texttospeech.v1beta1.ISynthesizeSpeechRequest,
+    request?: protos.google.cloud.texttospeech.v1beta1.ISynthesizeSpeechRequest,
     optionsOrCallback?:
       | CallOptions
       | Callback<