diff --git a/packages/google-cloud-documentai/src/v1/document_processor_service_client.ts b/packages/google-cloud-documentai/src/v1/document_processor_service_client.ts
index 578d2500d2f..91947a35a5f 100644
--- a/packages/google-cloud-documentai/src/v1/document_processor_service_client.ts
+++ b/packages/google-cloud-documentai/src/v1/document_processor_service_client.ts
@@ -137,6 +137,8 @@ export class DocumentProcessorServiceClient {
     }
     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/packages/google-cloud-documentai/src/v1beta1/document_understanding_service_client.ts b/packages/google-cloud-documentai/src/v1beta1/document_understanding_service_client.ts
index 8e404028c57..4e03441018e 100644
--- a/packages/google-cloud-documentai/src/v1beta1/document_understanding_service_client.ts
+++ b/packages/google-cloud-documentai/src/v1beta1/document_understanding_service_client.ts
@@ -135,6 +135,8 @@ export class DocumentUnderstandingServiceClient {
     }
     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/packages/google-cloud-documentai/src/v1beta2/document_understanding_service_client.ts b/packages/google-cloud-documentai/src/v1beta2/document_understanding_service_client.ts
index 2cd7490affd..e291f3059af 100644
--- a/packages/google-cloud-documentai/src/v1beta2/document_understanding_service_client.ts
+++ b/packages/google-cloud-documentai/src/v1beta2/document_understanding_service_client.ts
@@ -135,6 +135,8 @@ export class DocumentUnderstandingServiceClient {
     }
     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/packages/google-cloud-documentai/src/v1beta3/document_processor_service_client.ts b/packages/google-cloud-documentai/src/v1beta3/document_processor_service_client.ts
index 570cee2268f..877a98aae0d 100644
--- a/packages/google-cloud-documentai/src/v1beta3/document_processor_service_client.ts
+++ b/packages/google-cloud-documentai/src/v1beta3/document_processor_service_client.ts
@@ -137,6 +137,8 @@ export class DocumentProcessorServiceClient {
     }
     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}`);