diff --git a/tools_webrtc/mb/mb.py b/tools_webrtc/mb/mb.py
index a5f0e24608..45606ffbf4 100755
--- a/tools_webrtc/mb/mb.py
+++ b/tools_webrtc/mb/mb.py
@@ -96,6 +96,9 @@ class MetaBuildWrapper(object):
                         default=self.default_isolate_map,
                         help='path to isolate map file '
                              '(default is %(default)s)')
+      subp.add_argument('-r', '--realm', default='webrtc:try',
+                        help='optional LUCI realm to use (for '
+                             'example when triggering tasks on Swarming)')
       subp.add_argument('-g', '--goma-dir',
                         help='path to goma directory')
       subp.add_argument('--android-version-code',
@@ -390,6 +393,8 @@ class MetaBuildWrapper(object):
       cmd = [
           self.PathJoin('tools', 'luci-go', 'swarming'),
           'trigger',
+          '-realm',
+          self.args.realm,
           '-digest',
           cas_digest,
           '-server',