diff --git a/packages/google-cloud-kms/src/v1/key_management_service_client.ts b/packages/google-cloud-kms/src/v1/key_management_service_client.ts
index ab432761b7d..68ecee4b662 100644
--- a/packages/google-cloud-kms/src/v1/key_management_service_client.ts
+++ b/packages/google-cloud-kms/src/v1/key_management_service_client.ts
@@ -155,6 +155,8 @@ export class KeyManagementServiceClient {
     }
     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}`);