diff --git a/endpoints/callbacks.py b/endpoints/callbacks.py
index 66bb79f08..a8bb05dbe 100644
--- a/endpoints/callbacks.py
+++ b/endpoints/callbacks.py
@@ -84,8 +84,15 @@ def conduct_oauth_login(service, user_id, username, email, metadata={}):
 
     # Try to create the user
     try:
-      valid = next(generate_valid_usernames(username))
-      to_login = model.create_federated_user(valid, email, service_name.lower(),
+      new_username = None
+      for valid in generate_valid_usernames(username):
+        if model.get_user_or_org(valid):
+          continue
+
+        new_username = valid
+        break
+
+      to_login = model.create_federated_user(new_username, email, service_name.lower(),
                                              user_id, set_password_notification=True,
                                              metadata=metadata)