diff --git a/readthedocs/proxito/views/serve.py b/readthedocs/proxito/views/serve.py
index a5fd2f56835..a9c7a3e5808 100644
--- a/readthedocs/proxito/views/serve.py
+++ b/readthedocs/proxito/views/serve.py
@@ -261,7 +261,11 @@ def get(self, request, proxito_path, template_name='404.html'):
         # If that doesn't work, attempt to serve the 404 of the current version (version_slug)
         # Secondly, try to serve the 404 page for the default version
         # (project.get_default_version())
-        for version_slug_404 in set([version_slug, final_project.get_default_version()]):
+        versions = [version_slug]
+        default_version_slug = final_project.get_default_version()
+        if default_version_slug != version_slug:
+            versions.append(default_version_slug)
+        for version_slug_404 in versions:
             for tryfile in ('404.html', '404/index.html'):
                 storage_root_path = final_project.get_storage_path(
                     type_='html',