diff --git a/lms/djangoapps/mobile_api/users/views.py b/lms/djangoapps/mobile_api/users/views.py
index 5e76caed63..e63a737f48 100644
--- a/lms/djangoapps/mobile_api/users/views.py
+++ b/lms/djangoapps/mobile_api/users/views.py
@@ -272,15 +272,13 @@ class UserCourseEnrollmentsList(APIView):
         Returns a list of courses enrolled by user.
         """
         queryset = CourseEnrollment.objects.all()
-        enrollments = list(
-            queryset.filter(
-                user__username=username,
-                is_active=True
-            ).order_by('created').reverse()
-        )
-        course_ids = [enrollment.course_id for enrollment in enrollments]
+        course_ids = set(queryset.values_list('course_id', flat=True))
         catalog_course_runs_against_course_keys = get_course_runs(course_ids, request.user)
 
+        enrollments = queryset.filter(
+            user__username=username,
+            is_active=True
+        ).order_by('created').reverse()
         org = request.query_params.get('org', None)
 
         return Response([