diff -Naur marshmallow-3.5.1.orig/docs/conf.py marshmallow-3.5.1/docs/conf.py
--- marshmallow-3.5.1.orig/docs/conf.py	2020-03-05 14:01:01.000000000 +0100
+++ marshmallow-3.5.1/docs/conf.py	2020-03-24 12:42:34.539237871 +0100
@@ -14,7 +14,6 @@
     "sphinx.ext.viewcode",
     "alabaster",
     "sphinx_issues",
-    "versionwarning.extension",
 ]
 
 primary_domain = "py"
@@ -87,28 +86,3 @@
         "searchbox.html",
     ],
 }
-
-# sphinx-version-warning config
-versionwarning_messages = {
-    "latest": (
-        "This document is for the development version. "
-        'For the stable version documentation, see <a href="/en/stable/">here</a>.'
-    ),
-    "stable": (
-        "This document is for the latest 3.x stable release. "
-        'For the 2.x documentation, see <a href="/en/2.x-line/">here</a>.'
-    ),
-    "2.x-line": (
-        "This document is for the 2.x release branch. "
-        'For the 3.x documentation, see <a href="/en/stable/">here</a>.'
-    ),
-}
-# Show warning at top of page
-versionwarning_body_selector = "div.document"
-# For debugging locally
-# versionwarning_project_version = 'latest'
-
-
-def setup(app):
-    # https://docs.readthedocs.io/en/latest/guides/adding-custom-css.html
-    app.add_stylesheet("css/versionwarning.css")