--- a/mozharness/mozilla/updates/balrog.py
+++ b/mozharness/mozilla/updates/balrog.py
@@ -35,17 +35,17 @@ class BalrogMixin(object):
             self.buildbot_properties.items(),
         )))
         self.dump_config(props_path, balrog_props)
         cmd = [
             self.query_exe("python"),
             submitter_script,
             "--build-properties", props_path,
             "--api-root", c["balrog_api_root"],
-            "--username", self.query_balrog_username(product),
+            "--username", self._query_balrog_username(product),
             "-t", release_type,
             "--credentials-file", credentials_file,
         ]
         if self._log_level_at_least(INFO):
             cmd.append("--verbose")
 
         self.info("Calling Balrog submission script")
         return_code = self.retry(