diff --git a/packages/client/src/classes/client.js b/packages/client/src/classes/client.js
index c91768d4d..1497ae1d8 100644
--- a/packages/client/src/classes/client.js
+++ b/packages/client/src/classes/client.js
@@ -38,7 +38,6 @@ class Client {
 
   setApiKey(apiKey) {
     this.auth = 'Bearer ' + apiKey;
-    this.setDefaultRequest('baseUrl', SENDGRID_BASE_URL);
 
     if (!this.isValidApiKey(apiKey)) {
       console.warn(`API key does not start with "${API_KEY_PREFIX}".`);
@@ -48,7 +47,9 @@ class Client {
   setTwilioEmailAuth(username, password) {
     const b64Auth = Buffer.from(username + ':' + password).toString('base64');
     this.auth = 'Basic ' + b64Auth;
-    this.setDefaultRequest('baseUrl', TWILIO_BASE_URL);
+    if (this.defaultRequest.baseUrl === SENDGRID_BASE_URL) {
+      this.setDefaultRequest('baseUrl', TWILIO_BASE_URL);
+    }
 
     if (!this.isValidTwilioAuth(username, password)) {
       console.warn('Twilio Email credentials must be non-empty strings.');
diff --git a/packages/client/src/client.spec.js b/packages/client/src/client.spec.js
index 65e0e5997..9a526f173 100644
--- a/packages/client/src/client.spec.js
+++ b/packages/client/src/client.spec.js
@@ -106,6 +106,23 @@ describe('setImpersonateSubuser', () => {
   });
 });
 
+describe('setDefaultRequest', () => {
+  const customBaseUrl = 'localhost:3030';
+  const sgClient = require('./client');
+
+  it('should set the custom base URL without being overwritten by setApiKey', () => {
+    sgClient.setDefaultRequest('baseUrl', customBaseUrl);
+    sgClient.setApiKey('SG\.1234567890');
+    expect(sgClient.defaultRequest.baseUrl).to.equal(customBaseUrl);
+  });
+
+  it('should set the custom base URL without being overwritten by setTwilioEmailAuth', () => {
+    sgClient.setDefaultRequest('baseUrl', customBaseUrl);
+    sgClient.setTwilioEmailAuth('username', 'password');
+    expect(sgClient.defaultRequest.baseUrl).to.equal(customBaseUrl);
+  });
+});
+
 describe('test_access_settings_activity_get', () => {
   const request = {};
   request.qs = {