diff --git a/src/drf_yasg/management/commands/generate_swagger.py b/src/drf_yasg/management/commands/generate_swagger.py
index acc65b3..881b097 100644
--- a/src/drf_yasg/management/commands/generate_swagger.py
+++ b/src/drf_yasg/management/commands/generate_swagger.py
@@ -131,7 +131,7 @@ class Command(BaseCommand):
         if user:
             # Only call get_user_model if --user was passed in order to
             # avoid crashing if auth is not configured in the project
-            user = get_user_model().objects.get(username=user)
+            user = get_user_model().objects.get(**{get_user_model().USERNAME_FIELD: user})
 
         mock = mock or private or (user is not None) or (api_version is not None)
         if mock and not api_url: