diff --git a/appengine/standard/endpoints-frameworks-v2/backend/main.py b/appengine/standard/endpoints-frameworks-v2/backend/main.py
index 2348e1f6edc8..6b5feeefbf52 100644
--- a/appengine/standard/endpoints-frameworks-v2/backend/main.py
+++ b/appengine/standard/endpoints-frameworks-v2/backend/main.py
@@ -53,7 +53,9 @@ def echo(self, request):
         path='echo/getUserEmail',
         http_method='GET',
         # Require auth tokens to have the following scopes to access this API.
-        scopes=[endpoints.EMAIL_SCOPE])
+        scopes=[endpoints.EMAIL_SCOPE],
+        # OAuth2 audiences allowed in incoming tokens.
+        audiences='your-oauth-client-id.com')
     def get_user_email(self, request):
         user = endpoints.get_current_user()
         # If there's no user defined, the request was unauthenticated, so we