--- a/testing/mozharness/mozharness/mozilla/building/buildbase.py
+++ b/testing/mozharness/mozharness/mozilla/building/buildbase.py
@@ -1640,16 +1640,22 @@ or run without that action (ie: --no-{ac
             return
         self._initialize_taskcluster()
 
         dirs = self.query_abs_dirs()
         base_work_dir = dirs['base_work_dir']
         objdir = dirs['abs_obj_dir']
         branch = self.branch
 
+        # Building a nightly with the try repository fails because a
+        # config-file does not exist for try. Default to mozilla-central
+        # settings (arbitrarily).
+        if branch == 'try':
+            branch = 'mozilla-central'
+
         # Some android versions share the same .json config - if
         # multi_locale_config_platform is set, use that the .json name;
         # otherwise, use the buildbot platform.
         default_platform = self.buildbot_config['properties'].get('platform',
                                                                   'android')
 
         multi_config_pf = self.config.get('multi_locale_config_platform',
                                           default_platform)