diff --git a/examples/generated/proto/examplecom/simple_service_pb_service.js b/examples/generated/proto/examplecom/simple_service_pb_service.js
index 14a5a407..bee0f019 100644
--- a/examples/generated/proto/examplecom/simple_service_pb_service.js
+++ b/examples/generated/proto/examplecom/simple_service_pb_service.js
@@ -77,7 +77,10 @@ SimpleServiceClient.prototype.doUnary = function doUnary(requestMessage, metadat
     onEnd: function (response) {
       if (callback) {
         if (response.status !== grpc.Code.OK) {
-          callback(Object.assign(new Error(response.statusMessage), { code: response.status, metadata: response.trailers }), null);
+          var err = new Error(response.statusMessage);
+          err.code = response.status;
+          err.metadata = response.trailers;
+          callback(err, null);
         } else {
           callback(null, response.message);
         }
@@ -224,7 +227,10 @@ SimpleServiceClient.prototype.delete = function pb_delete(requestMessage, metada
     onEnd: function (response) {
       if (callback) {
         if (response.status !== grpc.Code.OK) {
-          callback(Object.assign(new Error(response.statusMessage), { code: response.status, metadata: response.trailers }), null);
+          var err = new Error(response.statusMessage);
+          err.code = response.status;
+          err.metadata = response.trailers;
+          callback(err, null);
         } else {
           callback(null, response.message);
         }
diff --git a/examples/generated/proto/orphan_pb_service.js b/examples/generated/proto/orphan_pb_service.js
index 979be1ea..f2f6c77e 100644
--- a/examples/generated/proto/orphan_pb_service.js
+++ b/examples/generated/proto/orphan_pb_service.js
@@ -48,7 +48,10 @@ OrphanServiceClient.prototype.doUnary = function doUnary(requestMessage, metadat
     onEnd: function (response) {
       if (callback) {
         if (response.status !== grpc.Code.OK) {
-          callback(Object.assign(new Error(response.statusMessage), { code: response.status, metadata: response.trailers }), null);
+          var err = new Error(response.statusMessage);
+          err.code = response.status;
+          err.metadata = response.trailers;
+          callback(err, null);
         } else {
           callback(null, response.message);
         }
diff --git a/src/service/grpcweb.ts b/src/service/grpcweb.ts
index b08a070f..d79b1af8 100644
--- a/src/service/grpcweb.ts
+++ b/src/service/grpcweb.ts
@@ -334,7 +334,10 @@ function printUnaryStubMethod(printer: CodePrinter, method: RPCMethodDescriptor)
                  .printLn(`onEnd: function (response) {`)
           .indent().printLn(`if (callback) {`)
             .indent().printLn(`if (response.status !== grpc.Code.OK) {`)
-              .indent().printLn(`callback(Object.assign(new Error(response.statusMessage), { code: response.status, metadata: response.trailers }), null);`)
+              .indent().printLn(`var err = new Error(response.statusMessage);`)
+                       .printLn(`err.code = response.status;`)
+                       .printLn(`err.metadata = response.trailers;`)
+                       .printLn(`callback(err, null);`)
             .dedent().printLn(`} else {`)
               .indent().printLn(`callback(null, response.message);`)
             .dedent().printLn(`}`)