diff --git a/packages/grpc-native-core/index.js b/packages/grpc-native-core/index.js
index 9534c7d4f..e9053e8a0 100644
--- a/packages/grpc-native-core/index.js
+++ b/packages/grpc-native-core/index.js
@@ -161,6 +161,9 @@ exports.loadPackageDefinition = function loadPackageDefintion(packageDef) {
   for (const serviceFqn in packageDef) {
     const service = packageDef[serviceFqn];
     const nameComponents = serviceFqn.split('.');
+    if (nameComponents.some(comp => comp === '__proto__')) {
+      continue;
+    }
     const serviceName = nameComponents[nameComponents.length-1];
     let current = result;
     for (const packageName of nameComponents.slice(0, -1)) {
diff --git a/packages/grpc-native-core/src/client.js b/packages/grpc-native-core/src/client.js
index faba6decb..7ca1aece5 100644
--- a/packages/grpc-native-core/src/client.js
+++ b/packages/grpc-native-core/src/client.js
@@ -992,6 +992,9 @@ exports.makeClientConstructor = function(methods, serviceName,
 
   Object.keys(methods).forEach(name => {
     const attrs = methods[name];
+    if (name === '__proto__') {
+      return;
+    }
     if (name.indexOf('$') === 0) {
       throw new Error('Method names cannot start with $');
     }
@@ -1011,7 +1014,7 @@ exports.makeClientConstructor = function(methods, serviceName,
     ServiceClient.prototype.$method_names[attrs.path] = name;
     // Associate all provided attributes with the method
     Object.assign(ServiceClient.prototype[name], attrs);
-    if (attrs.originalName) {
+    if (attrs.originalName && attrs.originalName !== '__proto__') {
       ServiceClient.prototype[attrs.originalName] =
         ServiceClient.prototype[name];
     }
diff --git a/packages/grpc-native-core/test/prototype_pollution_test.js b/packages/grpc-native-core/test/prototype_pollution_test.js
new file mode 100644
index 000000000..57b3d0b52
--- /dev/null
+++ b/packages/grpc-native-core/test/prototype_pollution_test.js
@@ -0,0 +1,27 @@
+/*
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+import * as assert from 'assert';
+
+const grpc = require('../');
+
+describe('loadPackageDefinition', () => {
+  it('Should not allow prototype pollution', () => {
+      grpc.loadPackageDefinition({'__proto__.polluted': true});
+      assert.notStrictEqual({}.polluted, true);
+  });
+});
\ No newline at end of file