diff --git a/packages/nicolium/src/locales/en.json b/packages/nicolium/src/locales/en.json
index 3a10ad624..9ba4f9e8e 100644
--- a/packages/nicolium/src/locales/en.json
+++ b/packages/nicolium/src/locales/en.json
@@ -1416,7 +1416,8 @@
   "login.otp_log_in.fail": "Invalid code, please try again.",
   "login.reset_password_hint": "Trouble logging in?",
   "login.sign_in": "Sign in",
-  "login_external.errors.instance_fail": "The instance returned an error.",
+  "login_external.errors.cors_fail": "Connection failed, likely due to CORS configuration. Is the instance configured to allow logins from other origins?",
+  "login_external.errors.instance_fail": "The instance returned an error. Is the URL correct?",
   "login_external.errors.network_fail": "Connection failed. Is a browser extension blocking it?",
   "login_form.divider": "or",
   "login_form.external": "Sign in from remote instance",
diff --git a/packages/nicolium/src/pages/auth/components/external-login-form.tsx b/packages/nicolium/src/pages/auth/components/external-login-form.tsx
index a8402458e..3e93c2eb6 100644
--- a/packages/nicolium/src/pages/auth/components/external-login-form.tsx
+++ b/packages/nicolium/src/pages/auth/components/external-login-form.tsx
@@ -13,7 +13,12 @@ const messages = defineMessages({
   instancePlaceholder: { id: 'login.fields.instance_placeholder', defaultMessage: 'example.com' },
   instanceFailed: {
     id: 'login_external.errors.instance_fail',
-    defaultMessage: 'The instance returned an error.',
+    defaultMessage: 'The instance returned an error. Is the URL correct?',
+  },
+  corsFailed: {
+    id: 'login_external.errors.cors_fail',
+    defaultMessage:
+      'Connection failed, likely due to CORS configuration. Is the instance configured to allow logins from other origins?',
   },
   networkFailed: {
     id: 'login_external.errors.network_fail',
@@ -47,8 +52,10 @@ const ExternalLoginForm: React.FC = () => {
         console.error(error);
         const status = error.response?.status;
 
-        if (status) {
+        if (status || !error.message) {
           toast.error(intl.formatMessage(messages.instanceFailed));
+        } else if (error.message === 'NetworkError when attempting to fetch resource.') {
+          toast.error(intl.formatMessage(messages.corsFailed));
         } else if (!status && ['Network request failed', 'Timeout'].includes(error.message)) {
           toast.error(intl.formatMessage(messages.networkFailed));
         }