diff --git a/app/javascript/src/javascripts/common.js b/app/javascript/src/javascripts/common.js.erb
similarity index 66%
rename from app/javascript/src/javascripts/common.js
rename to app/javascript/src/javascripts/common.js.erb
index e1d8c3065..24c033dea 100644
--- a/app/javascript/src/javascripts/common.js
+++ b/app/javascript/src/javascripts/common.js.erb
@@ -19,6 +19,14 @@ $(function() {
     $('#notice').fadeOut("fast");
     e.preventDefault();
   });
+
+  const CANONICAL_DOMAIN = <%= Danbooru.config.domain.to_json.html_safe %>;
+  const CANONICAL_HOSTNAME = <%= Danbooru.config.hostname.to_json.html_safe %>;
+  const ENABLE_ANTIPROXYING = <%= Danbooru.config.enable_antiproxying?.to_json.html_safe %>;
+
+  if (ENABLE_ANTIPROXYING && !location.hostname.endsWith(CANONICAL_DOMAIN)) {
+    location.hostname = CANONICAL_HOSTNAME;
+  }
 });
 
 window.submitInvisibleRecaptchaForm = function () {
diff --git a/config/danbooru_default_config.rb b/config/danbooru_default_config.rb
index 999319cff..21444300c 100644
--- a/config/danbooru_default_config.rb
+++ b/config/danbooru_default_config.rb
@@ -25,11 +25,16 @@ module Danbooru
       "Danbooru"
     end
 
-    # The canonical hostname of the site.
+    # The canonical hostname for the site, e.g. danbooru.donmai.us.
     def hostname
       Socket.gethostname
     end
 
+    # The canonical base domain for the site, e.g. donmai.us.
+    def domain
+      hostname
+    end
+
     # Contact email address of the admin.
     def contact_email
       "webmaster@#{hostname}"
@@ -551,6 +556,11 @@ module Danbooru
     def redis_url
       "redis://localhost:6379"
     end
+
+    # Try to prevent copycat sites from proxying our site and inserting ads or phishing passwords.
+    def enable_antiproxying?
+      Rails.env.production?
+    end
   end
 
   class EnvironmentConfiguration