diff --git a/src/v1/text_to_speech_client.ts b/src/v1/text_to_speech_client.ts
index d0065cc5..b7d655e6 100644
--- a/src/v1/text_to_speech_client.ts
+++ b/src/v1/text_to_speech_client.ts
@@ -130,6 +130,8 @@ export class TextToSpeechClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v1beta1/text_to_speech_client.ts b/src/v1beta1/text_to_speech_client.ts
index 81624106..56094247 100644
--- a/src/v1beta1/text_to_speech_client.ts
+++ b/src/v1beta1/text_to_speech_client.ts
@@ -130,6 +130,8 @@ export class TextToSpeechClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);