diff --git a/_plugins/siteurl.rb b/_plugins/siteurl.rb
new file mode 100644
index 000000000..0a1c812f4
--- /dev/null
+++ b/_plugins/siteurl.rb
@@ -0,0 +1,17 @@
+Jekyll::Hooks.register :site, :after_init do |site|
+  # Federalist will set the BRANCH environment variable when it's building a
+  # preview deployment. If the branch is nil (unset) or "main", do nothing. But
+  # for preview builds, set site.url to nil. If we don't do that, then site.url
+  # will be used by the jekyll-redirect-from plugin when it rewrites redirects,
+  # which will link AWAY from the preview site and to the production site,
+  # making it functionally impossible to preview the redirected page. Further,
+  # because the production and preview sites have different site.baseurl values,
+  # the redirect will go to a location that does not exist in production, so
+  # it'll just cause a 404.
+  #
+  # We can avoid all that by just emptying the site.url value on preview builds.
+  branch = ENV['BRANCH']
+  if !(branch.nil? || branch == 'main')
+    site.config['url'] = nil
+  end
+end