diff --git a/common/djangoapps/enrollment/tests/test_views.py b/common/djangoapps/enrollment/tests/test_views.py
index 7409923bd4..b65b61b30d 100644
--- a/common/djangoapps/enrollment/tests/test_views.py
+++ b/common/djangoapps/enrollment/tests/test_views.py
@@ -92,15 +92,15 @@ class EnrollmentTestMixin(object):
 
                 if expected_status == status.HTTP_200_OK:
                     data = json.loads(response.content)
-                    self.assertEqual(course_id, data['course_details']['course_id'])
+                    self.assertEqual(course_id, data['enrollment_detail']['course_details']['course_id'])
 
                     if mode is not None:
-                        self.assertEqual(mode, data['mode'])
+                        self.assertEqual(mode, data['enrollment_detail']['mode'])
 
                     if is_active is not None:
-                        self.assertEqual(is_active, data['is_active'])
+                        self.assertEqual(is_active, data['enrollment_detail']['is_active'])
                     else:
-                        self.assertTrue(data['is_active'])
+                        self.assertTrue(data['enrollment_detail']['is_active'])
 
                     if as_server:
                         # Verify that an audit message was logged.
@@ -503,7 +503,11 @@ class EnrollmentTest(EnrollmentTestMixin, ModuleStoreTestCase, APITestCase):
     def test_enrollment_already_enrolled(self):
         response = self.assert_enrollment_status()
         repeat_response = self.assert_enrollment_status(expected_status=status.HTTP_200_OK)
-        self.assertEqual(json.loads(response.content), json.loads(repeat_response.content))
+        response_enrollment_detail = json.loads(response.content)
+        repeat_response_enrollment_detail = json.loads(repeat_response.content)
+        self.assertEqual(
+            response_enrollment_detail['enrollment_detail'], repeat_response_enrollment_detail['enrollment_detail']
+        )
 
     def test_get_enrollment_with_invalid_key(self):
         resp = self.client.post(
diff --git a/common/djangoapps/enrollment/views.py b/common/djangoapps/enrollment/views.py
index ec84e5ee8c..1952b8346d 100644
--- a/common/djangoapps/enrollment/views.py
+++ b/common/djangoapps/enrollment/views.py
@@ -600,7 +600,7 @@ class EnrollmentListView(APIView, ApiKeyPermissionMixIn):
                     log.warning(msg)
                     return Response(status=status.HTTP_400_BAD_REQUEST, data={"message": msg})
 
-                response = api.update_enrollment(
+                enrollment_detail = api.update_enrollment(
                     username,
                     unicode(course_id),
                     mode=mode,
@@ -609,20 +609,28 @@ class EnrollmentListView(APIView, ApiKeyPermissionMixIn):
                 )
             else:
                 # Will reactivate inactive enrollments.
-                response = api.add_enrollment(username, unicode(course_id), mode=mode, is_active=is_active)
+                enrollment_detail = api.add_enrollment(username, unicode(course_id), mode=mode, is_active=is_active)
 
             email_opt_in = request.data.get('email_opt_in', None)
             if email_opt_in is not None:
                 org = course_id.org
                 update_email_opt_in(request.user, org, email_opt_in)
 
-            return Response(response)
+            return Response(
+                status=status.HTTP_200_OK,
+                data={
+                    "message": (
+                        u"The user [{username}] has already been enrolled in course run [{course_id}]."
+                    ).format(username=username, course_id=course_id),
+                    "enrollment_detail": enrollment_detail
+                }
+            )
         except CourseModeNotFoundError as error:
             return Response(
                 status=status.HTTP_400_BAD_REQUEST,
                 data={
                     "message": (
-                        u"The course mode '{mode}' is not available for course '{course_id}'."
+                        u"The [{mode}] course mode is expired or otherwise unavailable for course run [{course_id}]."
                     ).format(mode=mode, course_id=course_id),
                     "course_details": error.data
                 })
@@ -634,7 +642,15 @@ class EnrollmentListView(APIView, ApiKeyPermissionMixIn):
                 }
             )
         except CourseEnrollmentExistsError as error:
-            return Response(data=error.enrollment)
+            return Response(
+                status=status.HTTP_200_OK,
+                data={
+                    "message": (
+                        u"An enrollment already exists for user [{username}] in course run [{course_id}]."
+                    ).format(username=username, course_id=course_id),
+                    "enrollment_detail": error.enrollment
+                }
+            )
         except CourseEnrollmentError:
             return Response(
                 status=status.HTTP_400_BAD_REQUEST,