diff --git a/examples/generated/proto/examplecom/simple_service_pb_service.d.ts b/examples/generated/proto/examplecom/simple_service_pb_service.d.ts
index e925bea3..cb4ac5cb 100644
--- a/examples/generated/proto/examplecom/simple_service_pb_service.d.ts
+++ b/examples/generated/proto/examplecom/simple_service_pb_service.d.ts
@@ -62,7 +62,7 @@ export class SimpleService {
 
 export type ServiceError = { message: string, code: number; metadata: grpc.Metadata }
 export type Status = { details: string, code: number; metadata: grpc.Metadata }
-export type ServiceClientOptions = { transport: grpc.TransportConstructor; debug?: boolean }
+export type ServiceClientOptions = { transport?: grpc.TransportConstructor; debug?: boolean }
 
 interface UnaryResponse {
   cancel(): void;
diff --git a/examples/generated/proto/orphan_pb_service.d.ts b/examples/generated/proto/orphan_pb_service.d.ts
index c18e0ee8..ab177ea5 100644
--- a/examples/generated/proto/orphan_pb_service.d.ts
+++ b/examples/generated/proto/orphan_pb_service.d.ts
@@ -30,7 +30,7 @@ export class OrphanService {
 
 export type ServiceError = { message: string, code: number; metadata: grpc.Metadata }
 export type Status = { details: string, code: number; metadata: grpc.Metadata }
-export type ServiceClientOptions = { transport: grpc.TransportConstructor; debug?: boolean }
+export type ServiceClientOptions = { transport?: grpc.TransportConstructor; debug?: boolean }
 
 interface UnaryResponse {
   cancel(): void;
diff --git a/src/service/grpcweb.ts b/src/service/grpcweb.ts
index 79f18dda..f3eba851 100644
--- a/src/service/grpcweb.ts
+++ b/src/service/grpcweb.ts
@@ -204,7 +204,7 @@ function generateTypescriptDefinition(fileDescriptor: FileDescriptorProto, expor
 
   printer.printLn(`export type ServiceError = { message: string, code: number; metadata: grpc.Metadata }`);
   printer.printLn(`export type Status = { details: string, code: number; metadata: grpc.Metadata }`);
-  printer.printLn(`export type ServiceClientOptions = { transport: grpc.TransportConstructor; debug?: boolean }`);
+  printer.printLn(`export type ServiceClientOptions = { transport?: grpc.TransportConstructor; debug?: boolean }`);
   printer.printEmptyLn();
   printer.printLn("interface UnaryResponse {");
   printer.printIndentedLn("cancel(): void;");