diff --git a/lms/djangoapps/commerce/signals.py b/lms/djangoapps/commerce/signals.py
index 0d54ab4e7d..b135325dca 100644
--- a/lms/djangoapps/commerce/signals.py
+++ b/lms/djangoapps/commerce/signals.py
@@ -5,6 +5,7 @@ import logging
 from urlparse import urljoin
 
 from django.conf import settings
+from django.contrib.auth.models import AnonymousUser
 from django.core.mail import EmailMultiAlternatives
 from django.dispatch import receiver
 from django.utils.translation import ugettext as _
@@ -32,6 +33,13 @@ def handle_unenroll_done(sender, course_enrollment=None, skip_refund=False, **kw
     if course_enrollment and course_enrollment.refundable():
         try:
             request_user = get_request_user() or course_enrollment.user
+            if isinstance(request_user, AnonymousUser):
+                # Assume the request was initiated via server-to-server
+                # api call (presumably Otto).  In this case we cannot
+                # construct a client to call Otto back anyway, because
+                # the client does not work anonymously, and furthermore,
+                # there's certainly no need to inform Otto about this request.
+                return
             refund_seat(course_enrollment, request_user)
         except:  # pylint: disable=bare-except
             # don't assume the signal was fired with `send_robust`.
diff --git a/lms/djangoapps/commerce/tests/test_signals.py b/lms/djangoapps/commerce/tests/test_signals.py
index 85eb7cb591..014d572a57 100644
--- a/lms/djangoapps/commerce/tests/test_signals.py
+++ b/lms/djangoapps/commerce/tests/test_signals.py
@@ -1,6 +1,7 @@
 """
 Tests for signal handling in commerce djangoapp.
 """
+from django.contrib.auth.models import AnonymousUser
 from django.test import TestCase
 from django.test.utils import override_settings
 
@@ -109,6 +110,12 @@ class TestRefundSignal(TestCase):
         self.assertTrue(mock_refund_seat.called)
         self.assertEqual(mock_refund_seat.call_args[0], (self.course_enrollment, self.requester))
 
+        # HTTP user is another server (AnonymousUser): do not try to initiate a refund at all.
+        mock_get_request_user.return_value = AnonymousUser()
+        mock_refund_seat.reset_mock()
+        self.send_signal()
+        self.assertFalse(mock_refund_seat.called)
+
     @mock.patch('commerce.signals.log.warning')
     def test_not_authorized_warning(self, mock_log_warning):
         """