diff --git a/app/logical/note_sanitizer.rb b/app/logical/note_sanitizer.rb
index 27ca58345..9fa18cf3c 100644
--- a/app/logical/note_sanitizer.rb
+++ b/app/logical/note_sanitizer.rb
@@ -73,7 +73,20 @@ module NoteSanitizer
         at_rules: [],
         protocols: [],
         properties: ALLOWED_PROPERTIES,
-      }
+      },
+      :transformers => method(:relativize_links),
     )
   end
+
+  def self.relativize_links(node:, **env)
+    return unless node.name == "a" && node.attribute("href")
+
+    href = node.attribute("href")
+    url  = Addressable::URI.parse(href.value).normalize
+
+    if url.authority.in?(Danbooru.config.hostnames)
+      url.site = nil
+      href.value = url.to_s
+    end
+  end
 end
diff --git a/config/danbooru_default_config.rb b/config/danbooru_default_config.rb
index 662f79b71..bac24967e 100644
--- a/config/danbooru_default_config.rb
+++ b/config/danbooru_default_config.rb
@@ -20,11 +20,17 @@ module Danbooru
       "Find good anime art fast"
     end
 
-    # The hostname of the server.
+    # The canonical hostname of the site.
     def hostname
       Socket.gethostname
     end
 
+    # The list of all domain names this site is accessible under.
+    # Example: %w[danbooru.donmai.us sonohara.donmai.us hijiribe.donmai.us safebooru.donmai.us]
+    def hostnames
+      [hostname]
+    end
+
     # Contact email address of the admin.
     def contact_email
       "webmaster@#{server_host}"
diff --git a/test/unit/note_sanitizer_test.rb b/test/unit/note_sanitizer_test.rb
index e87ed67d7..bebacb3ae 100644
--- a/test/unit/note_sanitizer_test.rb
+++ b/test/unit/note_sanitizer_test.rb
@@ -21,5 +21,12 @@ class NoteSanitizerTest < ActiveSupport::TestCase
       body = '<a href="http://www.google.com">google</a>'
       assert_equal('<a href="http://www.google.com" rel="nofollow">google</a>', NoteSanitizer.sanitize(body))
     end
+
+    should "rewrite absolute links to relative links" do
+      Danbooru.config.stubs(:hostnames).returns(%w[danbooru.donmai.us sonohara.donmai.us hijiribe.donmai.us])
+
+      body = '<a href="http://sonohara.donmai.us/posts?tags=touhou#dtext-intro">touhou</a>'
+      assert_equal('<a href="/posts?tags=touhou#dtext-intro" rel="nofollow">touhou</a>', NoteSanitizer.sanitize(body))
+    end
   end
 end