diff --git a/readthedocs/core/views/__init__.py b/readthedocs/core/views/__init__.py
index 8fcccb749fb..a6d106fca18 100644
--- a/readthedocs/core/views/__init__.py
+++ b/readthedocs/core/views/__init__.py
@@ -145,7 +145,7 @@ def server_error_404_subdomain(request, template_name='404.html'):
     the Docs default page (Maze Found) is rendered by Django and served.
     """
 
-    def resolve_404_path(project, version_slug=None, language=None):
+    def resolve_404_path(project, version_slug=None, language=None, filename='404.html'):
         """
         Helper to resolve the path of ``404.html`` for project.
 
@@ -159,7 +159,7 @@ def resolve_404_path(project, version_slug=None, language=None):
             project,
             version_slug=version_slug,
             language=language,
-            filename='404.html',
+            filename=filename,
             subdomain=True,  # subdomain will make it a "full" path without a URL prefix
         )
 
@@ -197,16 +197,17 @@ def resolve_404_path(project, version_slug=None, language=None):
         # Firstly, 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 slug in (version_slug, project.get_default_version()):
-            basepath, filename, fullpath = resolve_404_path(project, slug, language)
-            if os.path.exists(fullpath):
-                log.debug(
-                    'serving 404.html page current version: [project: %s] [version: %s]',
-                    project.slug,
-                    slug,
-                )
-                r = static_serve(request, filename, basepath)
-                r.status_code = 404
-                return r
+            for tryfile in ('404.html', '404/index.html'):
+                basepath, filename, fullpath = resolve_404_path(project, slug, language, tryfile)
+                if os.path.exists(fullpath):
+                    log.debug(
+                        'serving 404.html page current version: [project: %s] [version: %s]',
+                        project.slug,
+                        slug,
+                    )
+                    r = static_serve(request, filename, basepath)
+                    r.status_code = 404
+                    return r
 
     # Finally, return the default 404 page generated by Read the Docs
     r = render(request, template_name)